RPetty2

Hey guys, I hope this thread can be humble and straight forward, in reverse and drive (going 3 mph) coasting my car will go like 700 rpm to 1300 and back and forth and after a few times it stalls and dies ? Is my idle to low? Thank you Ricky

jej3

Can you describe if when your engine was rebuilt if parts like the Idle Stabilizer Valve were replaced and/or if the Intake was refreshed?

Do you have the same problems when parked at idle?

Is this more noticable when the car is warm versus just starting?

Mine did this right before the LH and MAF both had to be rebuilt. I'm sure some of those smarter than me will chime in but answering the above questions will help them respond, I'm sure.

RPetty2

I had intake refresh on it and I put it in nutral before it dies and it goes back to normal

jej3

I'm sure there are several things it could be (most of which I might not know).

Do a search on Idle Stabilizer Valve or ISV. If it wasn't replaced, you might want to clean it with a cocktail of WD-40 and PBBlaster.

Since the engine was out of and now is back in the car, you may have a vacuum leak. Do a search on "vacuum leak idle" and I suspect you'll get some ideas.

Does it do this all the time or only when cold or only when warmed up?

Report back what you find and if people feel you're being civil, I'm sure they'll try to help you.

Just keep it together, kid and try not to flame anyone.

IcemanG17

2nd on the "WD40" trick for the idle stabilizer valve (ISV)...sharky had this problem.....but I would guess they cleaned it when they did the intake refresh?

RPetty2

That's what I was sayin, shouldn't it be cleaned like everything else, I'll look at my receipt to find something

IcemanG17

I cleaned mine using the WD40 trick and it helped the short term, but replacing it with a new one REALLY made it idle perfect!!!!

RPetty2

I won't
I'll play with stuff and post pics too
Thanks for ur Time

jej3

Come back with more info and read the isv cleaning threads. It is pretty easy to do.

Good luck!

linderpat

Also check the simple stuff first - this could be a vacume leak. Look at the lines, especially under the intake at the throttle body.

17prospective buyer

Is the car misfiring at all? Small vacuum leak sounds like a possibility. If there was a large leak post-MAF that might also cause it to run super lean causing a lean misfire. You can take your plugs out and usually tell roughly what A/F (if super lean or super rich) your engine cylinders are burning, i know that lean will usually leave a dry white deposit on the plugs, and positive electrode life will be decreased (from NOX production and high heat). Also as you're doing this make sure the right plugs are being used (heat range, plug gap, what the spark looks like if you ground it out and crank). Alot of misfiring issues that occur once operating temp has been reached is just because a DIY'er used a generic plug with the incorrect heat range, or the plug sticks out into the combustion chamber and heats up causing pre-ignition, i have seen this happen alot.

If it is a problem with one of your ECM inputs or feedbacks (O2 sensor) there are a few simple things you can do to diagnose. One of which is unplugging the O2 sensor while the car is running to see if it runs better in open loop. I don't think the ECM inputs located on the engine for speed/load/timing would be likely candidates since your engine was rebuilt. I'm pretty sure they would at least test all the sensors. Another big one is to unplug your MAF while car is running, this, AFAIK will trigger the ECM to sense no signal being received from the MAF and therefore defaulting to a safe AFM and separate fuel injection lookup table. This of course is to isolate the MAF to see if overly inaccurate signal voltage is affecting the idle.

It could also be a mechanical type problem in the fuel delivery/intake system, but that seems unlikely since if the engine builder was any good he would have noted down problem areas that need R&R attention.

I recommend going for a driveability test drive, and bringing a notepad and pencil with you. Be sure to record the startup conditions (eg. idle characteristics, idle characteristics in D and M modes and N, temp gauge level, etc), then as you drive note down any driveability issues (eg. engine vibration in D at standstill) and record when they occur and the conditions they occured in. It is easier to do this for a few drives, as sometimes you can notice patterns where the same condition occurs, making it much easier to pinpoint the source of the problem and what vehicle subsystem it is caused by.

Hopefully nothing electrical related, i hate those problems.

fraggle

If it is ok in neutral but not at in gear I'd start hunting vacuum leaks first. In gear you may have a leak, so the mixture gets wonked, the o2 sensor tries to adapt, the RPM's change, the leak then changes in magnitude, so it adjusts again, getting further and further out.

IcemanG17

Hmm....vacuum leaks are an easy check....all you need is a can of brake clean (ghetto method)

If Ricky brings his 928 to Thunderhill this weekend we will have plenty of time to diagnose when I'm not racing (only 2 hours-ish per day).....

dr bob

Make sure the throttle switch is working when the throttle is actually closed. Idle speed controller is only active when hat switch shows closed throttle. You can verify with an ohm meter at the LH connector.

IcemanG17

If I remember correctly the idle switch also has an audible "click".....or was that WOT....dammit....I haven't had an S4 in a bit