89 non cat hunting idle and cut out
04-27-2018, 04:12 AM
#1
Pro
Thread Starter
89 non cat hunting idle and cut out
Hi Guys
I know there are quite a few threads on bad idle which I searched however some were inconclusive and some were not. I started this one in the hope of throwing up a new fault or proving a fix.
The symptoms are that the car fires up ok but has a hunting idle and goes so low that it cuts out. I will try and take a video and post this also as it might help.
A further symptom is hesitation to the throttle being opened.
You can hear a lot of hissing which varies, I believe this is the ISV trying to stabilise the idle.
All this happened after a top end refresh / cam change.
The intake has been off and painted,
All the vacuum pipes from the ISV were inspected and are in good condition.
The ISV was tested and found to be working fine.
The TPS was tested and clicks as it should at the closed position (although this is a different switch on this manifold)
All injectors and spark plugs are new
I believe the issue to be a simple air leak from somewhere, it seemed to improve things slightly when I tightened up the connection on the side of the manifold which takes vacuum from near the throttle plate. The idle also seems to be affected by moving the MAF around.
The MAF is a rebuilt unit and the ECUs were working fine. The Hall sensor is new as are knock sensors etc. The cam timing was set with a Porken 32 tool.
I know there are quite a few threads on bad idle which I searched however some were inconclusive and some were not. I started this one in the hope of throwing up a new fault or proving a fix.
The symptoms are that the car fires up ok but has a hunting idle and goes so low that it cuts out. I will try and take a video and post this also as it might help.
A further symptom is hesitation to the throttle being opened.
You can hear a lot of hissing which varies, I believe this is the ISV trying to stabilise the idle.
All this happened after a top end refresh / cam change.
The intake has been off and painted,
All the vacuum pipes from the ISV were inspected and are in good condition.
The ISV was tested and found to be working fine.
The TPS was tested and clicks as it should at the closed position (although this is a different switch on this manifold)
All injectors and spark plugs are new
I believe the issue to be a simple air leak from somewhere, it seemed to improve things slightly when I tightened up the connection on the side of the manifold which takes vacuum from near the throttle plate. The idle also seems to be affected by moving the MAF around.
The MAF is a rebuilt unit and the ECUs were working fine. The Hall sensor is new as are knock sensors etc. The cam timing was set with a Porken 32 tool.
Last edited by Marti; 04-27-2018 at 05:07 AM.
04-27-2018, 04:19 AM
#2
Rennlist Member
Can you compress all of the intake hoses completely closed and not have them crack? If they crack they are old and warrant replacement. They often crack and leak when disturbed.
Otherwise it may be the boot that the maf connects to along with all the other hoses (more likely from your description). You may have cracked it if it was original. It is nearly 30 years old after all.
Otherwise it may be the boot that the maf connects to along with all the other hoses (more likely from your description). You may have cracked it if it was original. It is nearly 30 years old after all.
04-27-2018, 05:27 AM
#3
Pro
Thread Starter
Hi, responses below to your questions
Can you compress all of the intake hoses completely closed and not have them crack? Yes, I was ready to buy a new set until I checked them out, they must be a replacement set.If they crack they are old and warrant replacement. They often crack and leak when disturbed.
Otherwise it may be the boot that the maf connects to along with all the other hoses (more likely from your description). You may have cracked it if it was original. It is nearly 30 years old after all I also inspected the TB boot and although aged it looks ok, I am suspecting that the connections into that boot might be leaking as they didn’t feel particularly tight when fitting. I am going to try zip tying them to tighten them up as part of diagnosis .
Otherwise it may be the boot that the maf connects to along with all the other hoses (more likely from your description). You may have cracked it if it was original. It is nearly 30 years old after all I also inspected the TB boot and although aged it looks ok, I am suspecting that the connections into that boot might be leaking as they didn’t feel particularly tight when fitting. I am going to try zip tying them to tighten them up as part of diagnosis .
04-27-2018, 06:15 AM
#4
Rennlist Member
A few things you can test:
1. Isolate the tank vent connection that leads to that 3 way vent pipe that leads to the side of the oil filler neck [GB mentioned this the other day]. If the vent valve is open when it should be closed you will get false air at idle. Test to see if blanking off that connection modulates your problem.
2. The ISV, when it has no signal applied to it , defaults to a closed position with an air path that is calibrated to allow a fixed idle at the target idle speed with the a/c not engaged. If you can, try disengaging the idle speed connector and test what happens. If the engine is cold you will need to fether the throttle to get it to fire up and blip the throttle to keep it going. When the motor reaches correct operating temperature you should find it able to hold a stable idle close to the normal idle of 675 rpm give or take a bit. If you then switch on the a/c and the revs drop to about 500rpms and/or the motor cuts out then chances are the system does not have a leak. If there is a leak then the idle speed without the a/c] will be notably higher than normal.
3. The pipes on the side of manifold contain a venturi that pulls a vacuum irrespective of the throttle position. The pipes in that system must be air tight to avoid false air [you commented about this] and similarly, your brake servo must not be leaking air. If the servo or part of that system is leaking air, the passive vac reservoir [that feeds the flappy] will not evacuate correctly. Have you checked that the reservoir is holding vacuum as it should?
Oh, and nearly forgot to add- on my system I use jubillee clips on the nozzles on the side of the boot and the ISV pipes. Like yours, mine were a seemingly easy fit so I used some silicon RTV on the bosees and just nip the clamps- nothing gorilla style.
1. Isolate the tank vent connection that leads to that 3 way vent pipe that leads to the side of the oil filler neck [GB mentioned this the other day]. If the vent valve is open when it should be closed you will get false air at idle. Test to see if blanking off that connection modulates your problem.
2. The ISV, when it has no signal applied to it , defaults to a closed position with an air path that is calibrated to allow a fixed idle at the target idle speed with the a/c not engaged. If you can, try disengaging the idle speed connector and test what happens. If the engine is cold you will need to fether the throttle to get it to fire up and blip the throttle to keep it going. When the motor reaches correct operating temperature you should find it able to hold a stable idle close to the normal idle of 675 rpm give or take a bit. If you then switch on the a/c and the revs drop to about 500rpms and/or the motor cuts out then chances are the system does not have a leak. If there is a leak then the idle speed without the a/c] will be notably higher than normal.
3. The pipes on the side of manifold contain a venturi that pulls a vacuum irrespective of the throttle position. The pipes in that system must be air tight to avoid false air [you commented about this] and similarly, your brake servo must not be leaking air. If the servo or part of that system is leaking air, the passive vac reservoir [that feeds the flappy] will not evacuate correctly. Have you checked that the reservoir is holding vacuum as it should?
Oh, and nearly forgot to add- on my system I use jubillee clips on the nozzles on the side of the boot and the ISV pipes. Like yours, mine were a seemingly easy fit so I used some silicon RTV on the bosees and just nip the clamps- nothing gorilla style.
04-27-2018, 09:51 AM
#5
Nordschleife Master
Marti, if you apply throttle, does it stall, or does it go ok until you drop it to idle? If it stalls when you push the accelerator, then the MAF or it's connector harness would be the most likely culprit.
If not, then TPS and ISV are the next most likely.
TPS:
First off, make sure its adjusted so it clicks *every* time you release the throttle, even if you release the armature gently.
Second - make sure the click is actually electrical as well as audible. Disconnect the battery, unplug the LH, and measure at the pins on the connector to make sure its detecting idle correctly.
ISV:
Could be sticking - diagnosing that is hard.. so I just assume if everything else tests ok, that its sticking and hit it with the WD40 trick - my current '87 had this.
I assume you've already adjusted the CO pot to compensate for a new MAF? (otherwise it'll likely be running pig-rich)
If not, then TPS and ISV are the next most likely.
TPS:
First off, make sure its adjusted so it clicks *every* time you release the throttle, even if you release the armature gently.
Second - make sure the click is actually electrical as well as audible. Disconnect the battery, unplug the LH, and measure at the pins on the connector to make sure its detecting idle correctly.
ISV:
Could be sticking - diagnosing that is hard.. so I just assume if everything else tests ok, that its sticking and hit it with the WD40 trick - my current '87 had this.
I assume you've already adjusted the CO pot to compensate for a new MAF? (otherwise it'll likely be running pig-rich)
04-27-2018, 10:19 AM
#6
Pro
Thread Starter
Thanks Fred
I will be testing these suggestions over the next couple of days and reporting back. It is maybe no coincidence that when I wiggled the MAF in situ (attached to the rubber boot) that this affected the idle. I was very suspicious of those connections going into that rubber boot but keen to look at everything.
I will be testing these suggestions over the next couple of days and reporting back. It is maybe no coincidence that when I wiggled the MAF in situ (attached to the rubber boot) that this affected the idle. I was very suspicious of those connections going into that rubber boot but keen to look at everything.
04-27-2018, 10:27 AM
#7
Pro
Thread Starter
Hi, answers below in red, I am being more lead towards an air leak as I tested both the TPS and the ISV before fitting
Marti, if you apply throttle, does it stall, no, it picks up revs but hesitates or does it go ok until you drop it to idle? Idles roughly with some feathering of the throttle and stalls if you don’t apply throttle If it stalls when you push the accelerator, then the MAF or it's connector harness would be the most likely culprit.
If not, then TPS and ISV are the next most likely.
TPS:
First off, make sure its adjusted so it clicks *every* time you release the throttle, even if you release the armature gently.
Second - make sure the click is actually electrical as well as audible. Disconnect the battery, unplug the LH, and measure at the pins on the connector to make sure its detecting idle correctly.
ISV:
Could be sticking - diagnosing that is hard.. so I just assume if everything else tests ok, that its sticking and hit it with the WD40 trick - my current '87 had this.
I assume you've already adjusted the CO pot to compensate for a new MAF? CO pot was adjusted however injectors have now been changed to new 30lb design III injectors so could need adjusted again (otherwise it'll likely be running pig-rich)
If not, then TPS and ISV are the next most likely.
TPS:
First off, make sure its adjusted so it clicks *every* time you release the throttle, even if you release the armature gently.
Second - make sure the click is actually electrical as well as audible. Disconnect the battery, unplug the LH, and measure at the pins on the connector to make sure its detecting idle correctly.
ISV:
Could be sticking - diagnosing that is hard.. so I just assume if everything else tests ok, that its sticking and hit it with the WD40 trick - my current '87 had this.
I assume you've already adjusted the CO pot to compensate for a new MAF? CO pot was adjusted however injectors have now been changed to new 30lb design III injectors so could need adjusted again (otherwise it'll likely be running pig-rich)
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04-27-2018, 10:51 AM
#8
Rennlist Member
Thanks Fred
I will be testing these suggestions over the next couple of days and reporting back. It is maybe no coincidence that when I wiggled the MAF in situ (attached to the rubber boot) that this affected the idle. I was very suspicious of those connections going into that rubber boot but keen to look at everything.
I will be testing these suggestions over the next couple of days and reporting back. It is maybe no coincidence that when I wiggled the MAF in situ (attached to the rubber boot) that this affected the idle. I was very suspicious of those connections going into that rubber boot but keen to look at everything.
Marti,
Your response to Hilton about the behaviour sounds very much like the point [item 2] I raised as a test. This is what happens if the ISV connector is not fully home or there is a discontinuity of some kind in the circuit. I think there is a test in the WSM where you can manually load the ISV in situ to see if it is responding.If the idle with no a/c stabilises when the motor if fully warmed then the ISV is just not connected or not working. Whether the "MAF wiggle" can explain this I do not know but anything that modulates the issue has to be considered.
The MAF connector is also a point that can end up like a dog's breakfast. The boot is probably toast and will likely fall apart if you try to pull it back but if it is that bad then it needs replacing anyway. Mine was in such condition and I dealt with it by cutting the sleeving [that is probably solid by now] and then cut the cables in the main run where they looked to be in good condition and thus had some room to work in. Some of my cables had damage to the outer sheath and I covered them with a small diameter silicon tube to act as insulation- I made this "temporary fix" about 3 years ago and it is still working fine but next cool season I intend to cut out the crimp connections I made back to the harness and fit a new connector/boot/cores.
If you are running 30lb injectors presumably you have corrected for this in ST2?
04-27-2018, 07:08 PM
#9
Pro
Thread Starter
Minor break through, I found the plastic y pipe at the charcoal filter to have one connection snapped clean off.
I will need to order a new one and try it to see if this is what caused the problem.
I will need to order a new one and try it to see if this is what caused the problem.
04-27-2018, 07:38 PM
#10
Rennlist Member
I think someone offers a solution in metal- that or a chap of your resource can make one.
04-28-2018, 05:46 AM
#13
Rennlist Member
The hunting revs at idle show the idle loop is being activated but cannot reach equilibrium idle speed. Out of the idle loop range. Hunting means LH and ISV and TPS are most likely OK.
I suspect an idle leak.
I suspect an idle leak.
04-28-2018, 07:08 AM
#14
Nordschleife Master
More info on Marti's symptoms here: https://rennlist.com/forums/928-foru...l#post14971245
04-28-2018, 07:25 PM
#15
Pro
Thread Starter
John, per his reply to my earlier post, it stalls if he doesn't apply throttle - the rough idle is with some throttle assistance.
More info on Marti's symptoms here: https://rennlist.com/forums/928-foru...l#post14971245
More info on Marti's symptoms here: https://rennlist.com/forums/928-foru...l#post14971245
I am checking the air leak theory first and reporting back.
Many thanks