Idle Dive Bomb...
Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
Idle Dive Bomb...
Sorry - X-post over in the Turbo forum...meant to post over here to get a few more eyes on it and it's not turbo specific, at least I don't think...
I finally have my 951 running like a top. In recent weeks...a new Vitesse MAF and Tial 38mm. Pulls hard and runs great.
I don't have an idle issue at all. Car starts up great, never studders, pops right to about 850RPM and doesn't bounce around even when cold.
In really any gear if I rev high to say around 4k RPM and then clutch it at the same time I let off the gas completely the idle dive bombs to 300-400RPM briefly then jump back up to normal idle. The higher the rev when then clutch goes in and the gas is off means more of a chance (not scientific testing just my observation thus far) of it dive bombing to 0 and stalling the car. I've been careful with it and make sure that I don't disengage the clutch with the throttle off anywhere over around 2500RPM as it won't stall there - but sometimes even that low will do the dive bomb but jump back up to normal idle.
Things I've done:
1) Checked the TPS - immediate click when I move the throttle cable - pretty sure that's OK.
2) Cleaned the ICV with carb cleaner in both holes...sprayed with a little compressed air then ran a little WD40 in there. Based on the fact that my idle is OK, I'm pretty sure that the ISV is doing it's job.
3) I have a new battery, new ignition coil, new wires and spark plugs with less than 1k miles on them
4) I have a new O2 sensor on the way. PO records show that the shop put in a new O2 sensor at 60k. I have 89k on my car now.
With my Vitesse MAF, I've been running a little rich so I'm taking a stab that maybe my O2 sensor is gummed up. I've got one coming from Paragon - going to swap it out and see if it makes a difference.
Assuming it doesn't - what else??
I finally have my 951 running like a top. In recent weeks...a new Vitesse MAF and Tial 38mm. Pulls hard and runs great.
I don't have an idle issue at all. Car starts up great, never studders, pops right to about 850RPM and doesn't bounce around even when cold.
In really any gear if I rev high to say around 4k RPM and then clutch it at the same time I let off the gas completely the idle dive bombs to 300-400RPM briefly then jump back up to normal idle. The higher the rev when then clutch goes in and the gas is off means more of a chance (not scientific testing just my observation thus far) of it dive bombing to 0 and stalling the car. I've been careful with it and make sure that I don't disengage the clutch with the throttle off anywhere over around 2500RPM as it won't stall there - but sometimes even that low will do the dive bomb but jump back up to normal idle.
Things I've done:
1) Checked the TPS - immediate click when I move the throttle cable - pretty sure that's OK.
2) Cleaned the ICV with carb cleaner in both holes...sprayed with a little compressed air then ran a little WD40 in there. Based on the fact that my idle is OK, I'm pretty sure that the ISV is doing it's job.
3) I have a new battery, new ignition coil, new wires and spark plugs with less than 1k miles on them
4) I have a new O2 sensor on the way. PO records show that the shop put in a new O2 sensor at 60k. I have 89k on my car now.
With my Vitesse MAF, I've been running a little rich so I'm taking a stab that maybe my O2 sensor is gummed up. I've got one coming from Paragon - going to swap it out and see if it makes a difference.
Assuming it doesn't - what else??
Last edited by choinga; Jun 23, 2009 at 07:48 PM.
Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
yeah, I've messed around with the screw in the past to set idle, but right now my idle is good so not sure what opening it all the way will accomplish other than making the car idle higher than what it's supposed to?
Former Vendor
Joined: Mar 2002
Posts: 6,885
Likes: 39
From: Atlanta
You need to set idle again (via Idle screw) with the MAF in place. More than likely your TPS is not sending the idle signal (it can be adjusted) and/or the ICV is not doing it's job.
The TPS IDLE switch must be checked at the DME.
Assuming there are no vacuum leaks. The O2 sensor affects the closed loop operation.
The TPS IDLE switch must be checked at the DME.
Assuming there are no vacuum leaks. The O2 sensor affects the closed loop operation.
Racer
Joined: Mar 2009
Posts: 487
Likes: 0
Your idle is good because the ISV is doing it's job... you need to set the idle adjustment screw with the ISV bypassed.
Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
I've done that - I followed the directions on Lindsey's site for setting the idle post-MAF install. I bypassed using the DME test port and set idle on the screw. From turned all the way in, I have to back mine out CCW about 2 turns to get to ~840 idle. Their site says something about most being a half turn? I'm at like 600RPM at a half turn of the screw?
Once the car is warm though, there isn't really a difference. When I disconnect the test ports the idle stays the same and doesn't hunt or bounce around.
How do you test the TPS at the DME? All I know is mine clicks immediately as soon as you put any tension on the throttle cable. I haven't seen/heard of any other way to test that. Obviously the connector has wires that run back there so assume it's checking a voltage or something. One of these days I'll get my PB installed...
FWIW, I didn't have this problem prior to the MAF install which was a Vitesse AFM w/ Accuboost configuration.
I do worry that the car running rich may have something to do with it. It hadn't run for several hours when I went out a few minutes ago and started it up. Immediately, my narrowband A/F gauge at warm idle showed 1 bar into green or 'rich' instead of mid-stoich like it did (it swept a lot at idle too prior to the MAF install - really never does that anymore) prior to the MAF. I know the MAF is designed to run a little rich, but I've even adjusted the FQS on the DME to a -5% fuel and it still appears I'm running rich. Then again, I'm no expert so that quite possibly could have absolutely nothing to do with my idle problem.
Anyway, I know it's always something with these cars...
Other than this little issue - I have no complaints. My car runs great...the MAF and Tial combonation is like driving a new car. Now, if I could just get this pesky idle bomb figured out I'd be good to go...
Once the car is warm though, there isn't really a difference. When I disconnect the test ports the idle stays the same and doesn't hunt or bounce around.
How do you test the TPS at the DME? All I know is mine clicks immediately as soon as you put any tension on the throttle cable. I haven't seen/heard of any other way to test that. Obviously the connector has wires that run back there so assume it's checking a voltage or something. One of these days I'll get my PB installed...
FWIW, I didn't have this problem prior to the MAF install which was a Vitesse AFM w/ Accuboost configuration.
I do worry that the car running rich may have something to do with it. It hadn't run for several hours when I went out a few minutes ago and started it up. Immediately, my narrowband A/F gauge at warm idle showed 1 bar into green or 'rich' instead of mid-stoich like it did (it swept a lot at idle too prior to the MAF install - really never does that anymore) prior to the MAF. I know the MAF is designed to run a little rich, but I've even adjusted the FQS on the DME to a -5% fuel and it still appears I'm running rich. Then again, I'm no expert so that quite possibly could have absolutely nothing to do with my idle problem.
Anyway, I know it's always something with these cars...
Other than this little issue - I have no complaints. My car runs great...the MAF and Tial combonation is like driving a new car. Now, if I could just get this pesky idle bomb figured out I'd be good to go...
Drifting
Joined: Jan 2004
Posts: 2,023
Likes: 2
From: Michigan
You need to set idle again (via Idle screw) with the MAF in place. More than likely your TPS is not sending the idle signal (it can be adjusted) and/or the ICV is not doing it's job.
The TPS IDLE switch must be checked at the DME.
Assuming there are no vacuum leaks. The O2 sensor affects the closed loop operation.
The TPS IDLE switch must be checked at the DME.
Assuming there are no vacuum leaks. The O2 sensor affects the closed loop operation.
These are exactly the points I was going to say when I read the post. You MUST disable the ICV to adjust the idle. Otherwise the ECU will attempt to keep the idle electronically control through the TPS until it goes out of range.
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Drifting
Joined: Jan 2004
Posts: 2,023
Likes: 2
From: Michigan
I've done that - I followed the directions on Lindsey's site for setting the idle post-MAF install. I bypassed using the DME test port and set idle on the screw. From turned all the way in, I have to back mine out CCW about 2 turns to get to ~840 idle. There site says something about most being a half turn?
Once the car is warm though, there isn't really a difference. When I disconnect the test ports the idle stays the same and doesn't hunt or bounce around.
How do you test the TPS at the DME? All I know is mine clicks immediately as soon as you put any tension on the throttle cable.
FWIW, I didn't have this problem prior to the MAF install which was a Vitesse AFM w/ Accuboost configuration.
I do worry that the car running rich may have something to do with it. It hadn't run for several hours when I went out a few minutes ago and started it up. Immediately, my narrowband A/F gauge at warm idle showed 1 bar into green or 'rich' instead of mid-stoich like it did (it swept a lot at idle too prior to the MAF install - really never does that anymore) prior to the MAF. I know the MAF is designed to run a little rich, but I've even adjusted the FQS on the DME to a -5% fuel and it still appears I'm running rich. Then again, I'm no expert so that quite possibly could have absolutely nothing to do with my idle problem.
Anyway, I know it's always something with these cars... Other than this little issue - I have no complaints. My car runs great...the MAF and Tial combonation is like driving a new car. Now, if I could just get this pesky idle bomb figured out I'd be good to go...
Once the car is warm though, there isn't really a difference. When I disconnect the test ports the idle stays the same and doesn't hunt or bounce around.
How do you test the TPS at the DME? All I know is mine clicks immediately as soon as you put any tension on the throttle cable.
FWIW, I didn't have this problem prior to the MAF install which was a Vitesse AFM w/ Accuboost configuration.
I do worry that the car running rich may have something to do with it. It hadn't run for several hours when I went out a few minutes ago and started it up. Immediately, my narrowband A/F gauge at warm idle showed 1 bar into green or 'rich' instead of mid-stoich like it did (it swept a lot at idle too prior to the MAF install - really never does that anymore) prior to the MAF. I know the MAF is designed to run a little rich, but I've even adjusted the FQS on the DME to a -5% fuel and it still appears I'm running rich. Then again, I'm no expert so that quite possibly could have absolutely nothing to do with my idle problem.
Anyway, I know it's always something with these cars...
Other than this little issue - I have no complaints. My car runs great...the MAF and Tial combonation is like driving a new car. Now, if I could just get this pesky idle bomb figured out I'd be good to go...Trying warming up your car then unplug or disable the ISV then go for a drive to see if the idle it still dropping.
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Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
Hmmm...how do you test that? It seems to work fine...definitely moves around and goes rich when under load, etc... Are you saying that the AF gauge malfunctioning affects the way the car idles?
One other thing maybe worth mentioning...
If I sit in the garage with the car running but not moving and rev the engine, it never bombs...in fact most times it's almost like something 'catches' it around 2k RPM and slowly brings it back down to the correct idle. It only does the bomb when I'm out moving around at high rev with the clutch in and the gas out.
I just got confirmation from Paragon that my O2 sensor will be here tomorrow so I'll install that and see if that changes anything (primarily my rich problem) and I'll disable the ICV and see if I still bomb while in gear. Is it acceptable to use the test points on the DME for this purpose or do I need to actually pull the electrical harness off the ICV?
One other thing maybe worth mentioning...
If I sit in the garage with the car running but not moving and rev the engine, it never bombs...in fact most times it's almost like something 'catches' it around 2k RPM and slowly brings it back down to the correct idle. It only does the bomb when I'm out moving around at high rev with the clutch in and the gas out.
I just got confirmation from Paragon that my O2 sensor will be here tomorrow so I'll install that and see if that changes anything (primarily my rich problem) and I'll disable the ICV and see if I still bomb while in gear. Is it acceptable to use the test points on the DME for this purpose or do I need to actually pull the electrical harness off the ICV?
Rennlist Member
Joined: Jan 2002
Posts: 12,567
Likes: 548
From: Just CA Now :)
I went through this for a while with the Vitesse MAF and, despite swearing to the contrary after pressure testing, etc., it turned out to be a torn I/C coupler. I fixed that and it now falls right back to idle without a glitch just like a factory car. If it is a vacuum leak, it is probably worst when you floor it in a higher gear until say 3500-4000 rpms, then push in the clutch and let off the gas. Adding air to the idle can help it (or creating crazy maps in the piggyback), but those are just bandaids.
Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
Which I/C coupler? You mean the silicon or rubber piece that connects the IC pipe to the TB or intercooler itself? I put on Lindsey hard pipes with my MAF...they are all on there solid and I'm using their heavy duty clamps...nothing obvious thats leaking...not sure how to troubleshoot that...but my condition is exactly as you describe...get up to 3-4k RPM and take your foot off the gas and hit the clutch and instant dive bomb...and at that RPM I'd be lucky if the car kept running.
I haven't done any hard testing but I'll go out on a limb and say I'd be suprised if I have a vacuum leak - or at least not one big enough to have this effect. At cold idle I'm at 12-14hg and at warm idle I'm at 18-20hg on my boost gauge. All signs indicate that my vacuum pressure is good. Last time I had the intake off about a month ago I changed every vacuum line (including the big lines) in the engine with silicon lines.
How do 'add air' like you were saying - is that just cranking the idle screw out or something else? I experimented with that earlier...increased idle to a little under 1k RPM and it still bombed out.
I haven't done any hard testing but I'll go out on a limb and say I'd be suprised if I have a vacuum leak - or at least not one big enough to have this effect. At cold idle I'm at 12-14hg and at warm idle I'm at 18-20hg on my boost gauge. All signs indicate that my vacuum pressure is good. Last time I had the intake off about a month ago I changed every vacuum line (including the big lines) in the engine with silicon lines.
How do 'add air' like you were saying - is that just cranking the idle screw out or something else? I experimented with that earlier...increased idle to a little under 1k RPM and it still bombed out.
Drifting
Joined: Jan 2004
Posts: 2,023
Likes: 2
From: Michigan
Hmmm...how do you test that? It seems to work fine...definitely moves around and goes rich when under load, etc... Are you saying that the AF gauge malfunctioning affects the way the car idles?
One other thing maybe worth mentioning...
If I sit in the garage with the car running but not moving and rev the engine, it never bombs...in fact most times it's almost like something 'catches' it around 2k RPM and slowly brings it back down to the correct idle. It only does the bomb when I'm out moving around at high rev with the clutch in and the gas out.
I just got confirmation from Paragon that my O2 sensor will be here tomorrow so I'll install that and see if that changes anything (primarily my rich problem) and I'll disable the ICV and see if I still bomb while in gear. Is it acceptable to use the test points on the DME for this purpose or do I need to actually pull the electrical harness off the ICV?
One other thing maybe worth mentioning...
If I sit in the garage with the car running but not moving and rev the engine, it never bombs...in fact most times it's almost like something 'catches' it around 2k RPM and slowly brings it back down to the correct idle. It only does the bomb when I'm out moving around at high rev with the clutch in and the gas out.
I just got confirmation from Paragon that my O2 sensor will be here tomorrow so I'll install that and see if that changes anything (primarily my rich problem) and I'll disable the ICV and see if I still bomb while in gear. Is it acceptable to use the test points on the DME for this purpose or do I need to actually pull the electrical harness off the ICV?
What are you using for a BOV/Bypass Valve? It's not vent to the atmosphere is it? Have you checked the intake system for boost/vacuum leaks?
Disabling it at the test points would be the best way.
Rennlist Member
Joined: Jan 2002
Posts: 12,567
Likes: 548
From: Just CA Now :)
Which I/C coupler? Not sure I know what you are talking about...assuming that = vacuum leak?
I haven't done any hard testing but I doubt I have a vacuum leak anywhere - or at least not one big enough to have this effect. At cold idle I'm at 12-14hg and at warm idle I'm at 18-20hg on my boost gauge. All signs indicate that my vacuum pressure is good. Last time I had the intake off about a month ago I changed every vacuum line (including the big lines) in the engine with silicon lines.
I haven't done any hard testing but I doubt I have a vacuum leak anywhere - or at least not one big enough to have this effect. At cold idle I'm at 12-14hg and at warm idle I'm at 18-20hg on my boost gauge. All signs indicate that my vacuum pressure is good. Last time I had the intake off about a month ago I changed every vacuum line (including the big lines) in the engine with silicon lines.
By coupler, I mean the big hose connectors attaching the i/c pipes to the i/c and throttle body and turbo. They are not the only source of leaks, but they're common ones...
Thread Starter
Three Wheelin'
Joined: Dec 2008
Posts: 1,420
Likes: 2
From: Austin, TX
I'm using the Evo aluminum one from Lindsey. I assume it vents to the atmosphere - my car sounds like a Ruf Turbo now between shifts since I've installed the MAF. The vacuum port is connected of course and both of the other connections to the MAF pipe and IC pipe are solid and don't appear to be leaking - both connections are new hoses and new clamps.
The vacuum port is connected of course and both of the other connections to the MAF pipe and IC pipe are solid and don't appear to be leaking - both connections are new hoses and new clamps.