Doyle623

I can't seem to make this car happy at idle. I went through the idle reset procedure a few times and the car will idle around 840 rpm (as it should) when warm but the only difference I see when adjusting the idle screw is how fast the RPMs drop coming off of throttle. I have to turn the air screw out about 3 full turns for the RPMs to not drop so fast that they drop to 4-500 RPM and bog for a few seconds before rebounding. Another issue is when I first start the car (cold) it cranks 5-6 times, fires then dies after a couple of seconds (upon immediate start-up the car idles "ok"). I've bench tested the TPS and ICV and both seem to test ok. I checked the fuel pressure gauge (3 bar fpr) and its reading 40 psi with vac line attached and ~46 with vac line off. I have a Vitesse kit with Momonitor and the MAF voltage is showing .7 volts at idle, and coming off of throttle drops to about .5 before rebounding back to .7. I'll also add that I have to add fuel only to the idle cell on my SMT8 piggy back (+10 in cell zero). The car otherwise runs and drives nicely.

Do these signs point to a bad DME?

Tom M'Guinn

The ISV will fight against your screw adjustments to keep it at 840 if you don't bypass it in the diagnostic port. That said, I adjust the idle screw out as far as possible without falling out of range of the ISV (i.e., as high as you can without having the idle go above 840 with the ISV in closed loop). That helps prevent the idle from stumbling when quickly going from heavy boost to idle. On my car, however, the MAF voltage does not return to idle-level voltage after heavy boosting as fast as the RPMs drop, so is too high when the motor gets to 840, though it sounds like your MAF voltages are dropping too fast? Have you tried clocking the MAF in different orientations? That can sometimes help if the blowoff/bypass discharge is throwing the MAF off. Maybe post some logs... As is my way, I made my own piggyback that monitors the throttle position, MAF, and engine temp, and supplies just the right idle voltage in lieu of whatever the MAF is doing when quickly going from heavy load to idle -- which gives me a rock solid return to idle regardless. As for your tough starts, I wonder if the check valve in your fuel pump is leaking? Sounds like it is taking time to rebuild line pressure?

fast951

You have described multiple issues to deal with.
A- The cold start. We need more information for a better diagnostic. Start by observing the fuel pressure. As Tom suggested, you could be losing pressure.

B- The Idle issue.
- Assuming there are no vacuum leaks and you have the proper FQS set.
- First thing I noticed is the 0.7V MAF signal at idle. This is too high if idle is around 850rpm. Is this value measured before you increase the MAF voltage via PB?
- adding a value of 10 to the bottom left cell is not the proper way to adjust the MAF signal for what you are trying to accomplish. Go back to "0" value, and set the Analog#1 MIN value in the parameters screen. This will be the lowest MAF voltage that the DME sees.

The dip is not normal. It could be caused by many things, including but not limited to improper values in the PB. To eliminate possibilities, remove the PB and use the shorting/bypass plugs in its place. Now that you eliminated the PB, take a MoMonitor log of the problem. Carefully review it, by observing the throttle (should see idle switch). Look for anything odd, temp sensor value, MAF voltage off..

With PB still off, adjust your idle, by following the factory or Clark's-garage procedure.

If the issue remains, check your ICV and its circuit.

You should have a rock steady idle. Once you do, install the PB.

Humboldtgrin

Tom M'Guinn

Agreed. I should have mentioned that my motor is "special" in many ways, so everything it needs tends to be customized. On Crazy Eddie's car, which (despite the bling) is a stock 951 motor with the VR turbo and MAF, it truly idles and drives like a factory car -- rock solid idle, factory driveabilty, and pulls like a beast.

Doyle623

A) I went through the idle procedure again before my first start today and the RPMs dropped after firing, but didn't stall. Rather than turning the idle stop 1/8 turn, I turned it about 1/4 turn and clocked the MAF to 12, which seemed to help (with current parameters). I'll work on that once I get the idle set properly.

B) Once the car is warm I have 17 In Hg of vacuum per my ZT2 and Momonitor, but have not done a proper vacuum leak test. The 0.7 value is the what I'm seeing on the Momonitor. I started my car and on the SMT-8 I'm seeing AN 1 input 0.7 and the AN 1 output 0.7. I'm looking at the "Parameters" window and the the An1 lower limit is 0.30 (upper is 5.00).

Currently my FQS set at position 1 (+5%) and 10 in cell zero of the Analog 1 map. So far this is the only way I've gotten the car to behave at idle.
- At FQS position #1 and "0" in the first cell, my the AFR is around the mid 16's.
- At FQS position zero, and "0" in the first cell, my car will barely fire and die. (same for these setting with the shorting plug on the SMT8).

Before I move forward, should I have a different value for my lower analog limit?

Doyle623

Also, per the SMT8 my TPS Percent is ~15 at idle and the MoMonitor recognizes it as idle. Is this normal for the TPS percentage at ldle?

fast951

The TPS scale in the SMT8 is user definable. So the 15% could be 0-15%. As long a the Monitor is displaying the correct TPS state, your TPS is fine.

Tom M'Guinn

If you have 10 in the idle cells and yet the IN and OUT voltages shown in the SMT8 software is the same, then something isn't right there. Sure you are on the right map and cells? Sure it's wired and configured right?

Doyle623

Hi Tom, I'm sorry I think I mis-typed. What I meant was with the cells at "0", the in and out with the SMT8 were the same as the voltage with the shorting plug in its place. With 10 in the first block, the voltage out raises by ~0.1. I did find 2 leaks today, one at the idle valve (around the housing, which I've now sealed with JB weld) and the other at the thermo-valve. I'll address these and report back. Thanks for the input.

Doyle623

A quick update, I addressed my vacuum leaks, performed another idle reset, borrowed another good TPS, bench tested/sealed my ICV, and now at warm idle my MAF voltage is around .56-.58, but I still have to place the FQS at position 1 (+5%) and make my idle cell "10" to get the car to idle at 14.7. As previously mentioned, the car will not start at FQS position 0 and 0 in all analog cells. This is not a new problem for my car, as it was this way with the previous set-ups (both Vitesse and Autothority MAFs), I just figured it was due to old wiring. This spring I replaced every wiring harness that Lindsey Racing selling, which fixed some issues, but not the lean idle issue. My injectors, FPR, fuel damper, and ignition rotor are all new and fuel pressure at the rail looks to be correct for the 3 bar FPR. At this point, I'm thinking of sending my computers for a check-up.

Tom M'Guinn

Is the problem just at idle? What is the AFR like are part and full throttle with the SMT8 zero'd out?

Dan Martinic

Tom, doesn't this result in a hard jolt around 1200rpm when the fuel is re-introduced after off-throttle cut-off? Or does your (I assume) non-stock chip not do the fuel cut-off?

To the OP, my idle screw--completely stock system--is also out about 2.5-3 turns. This results in the same idle with ICV in or out (via diagnostic port jumper) and a near-perfect drop without the too-low dip and minimal "jolt" from fuel re-engagement.

I think it's near impossible to avoid either the "jolt" (ie. idle screw set too far out) or "dip" (idle screw too far in). Maybe there's a perfect spot where neither happens, but I can't find it lol

Doyle623

An update on my cold start issue of firing, then immediately stalling. I replaced my old DME with a FTech9 DME (very nice units), and although the idle was smoother overall, the stalling issue continued. I just finished the clutch job and in the process replaced my speed/reference sensors. It appears that the speed/ref. sensors were there culprit of the odd starting issue.

mahoney944

I have to run my vitesse vmaf+ kit at fqs 3 to idle at 14.7 as it has trouble starting and idles lean at 0% and +5% fuel. My vac lines are the bare min and are easy to check and have done so many times. The only thing I found is if I quickly pump the brakes on and off, my afr goes lean to about 16 for a few seconds. I traced this down to either the brake booster or the seal going into it where the check valve is. I thought, well that must be why I need to use fqs 3 but even with the brake booster capped off at the manifold, completely removing it from the vac system, (Which fixes the pumping the brakes going lean issue). I still need fqs 3 to idle properly. Though I see 10.8 at wot. Probably a bit rich but I'm still working on it.