running lean and rough idle after coming to stop

[eclipsegsx1736]

Ive noticed that often when I come to a stop and put in the clutch and the car goes down to idle, it idles a little rough (sometimes barely noticeable, sometimes swinging back and forth as low as 550) and my A/F gauge reads PEGGED lean, sometimes to the point where the last LED almost goes out. I know this is supposed to happen when youre off the gas and coasting, but not at idle. After about 5-10 secs of this rough lean idle, the car immediately starts idling perfectly again, and the A/F gauge resumes its normal bouncing back and forth. Ive tried richening the low end RPMs some on the AFC just to see if it helps, but it doesnt. Other than those 10 seconds after coming to a stop, it idles rock-solid. Any idea what this could be?

 

[GTM]

Ive noticed that often when I come to a stop and put in the clutch and the car goes down to idle, it idles a little rough (sometimes barely noticeable, sometimes swinging back and forth as low as 550) and my A/F gauge reads PEGGED lean, sometimes to the point where the last LED almost goes out. I know this is supposed to happen when youre off the gas and coasting, but not at idle.

What happens if you throw it into neutral with foot off clutch?

This is sounding a little like an EGR is acting up or a vacuum leak. Looking at your mods I take it you don't have a PCV valve installed? O2 sensor?

Cheers,
GTM

 

[cfisher]

I've been having the same problems for about 3 months and cannot find the source of the problem. I have a CEL code for my EGR valve which I have blocked off. I also have a CEL for my 2nd o2 sensor which I think has failed. I'm going to do the VFAQ mod on it so I don't have to worry about it anymore but I don't think that is what is causing this problem.

 

[Boost95]

Did you ever figure out your problem?

 

[kingjust]

Ive noticed that often when I come to a stop and put in the clutch and the car goes down to idle, it idles a little rough (sometimes barely noticeable, sometimes swinging back and forth as low as 550) and my A/F gauge reads PEGGED lean, sometimes to the point where the last LED almost goes out. I know this is supposed to happen when youre off the gas and coasting, but not at idle. After about 5-10 secs of this rough lean idle, the car immediately starts idling perfectly again, and the A/F gauge resumes its normal bouncing back and forth. Ive tried richening the low end RPMs some on the AFC just to see if it helps, but it doesnt. Other than those 10 seconds after coming to a stop, it idles rock-solid. Any idea what this could be?

Well the first of my concerns is that you said the idle drops when you put in the clutch... symptom of the infamous CW theory. With the AF, i'm not sure. There is nothing that the clutch does to effect AF, so i'm scratching my head on that. I'll keep thinking and let you know if I come up with any "outlandish" things... No, for real, if I do come up with something, I will post it!!

KJ

 

[Zenja]

My car started doing this too right after I replaced the starter a week ago and ran a new wire to the solenoid. It also has a tough time starting and running at first, but is good after getting warmed up. I can't see what would have caused it in my situation other than the wiring which I'll try reverting back to stock. Maybe I developed a vacuum leak or something though.

 

[kingjust]

My car started doing this too right after I replaced the starter a week ago and ran a new wire to the solenoid. It also has a tough time starting and running at first, but is good after getting warmed up. I can't see what would have caused it in my situation other than the wiring which I'll try reverting back to stock. Maybe I developed a vacuum leak or something though.

By changing your starter??? I can't see why, who knows... can some wisemen chime in on this one?

 

[Zenja]

I don't know. I wouldn't think about it too hard yet because it's likely to be unrelated. Changing the starter definitely wouldn't have done it, but I rewired the solenoid trigger wire and that affected some other electrical things for sure. For example, the fuel pump no longer turns on with the key in the start position. I thought the place I tapped into goes straight through the firewall to the solenoid, but it turns out there's other stuff in between. If reverting back to stock wiring fixes it, I'll mention it here so that it can give some clues about what type of stuff could be causing it.

 

[kingjust]

I don't know. I wouldn't think about it too hard yet because it's likely to be unrelated. Changing the starter definitely wouldn't have done it, but I rewired the solenoid trigger wire and that affected some other electrical things for sure. For example, the fuel pump no longer turns on with the key in the start position. I thought the place I tapped into goes straight through the firewall to the solenoid, but it turns out there's other stuff in between. If reverting back to stock wiring fixes it, I'll mention it here so that it can give some clues about what type of stuff could be causing it.

Just leave it stock until there is a place to tap that will not interfere with any of the selonoids... could be exactly what you said. Hope you get it resolved bro!!

 

[BoostFrenzy]

Haha, this sounds like MY car. . By any chance is this referring to it BBR?

I have the same symptoms. If this is referring to my car that I got, then it is still doing it but only occasionally. I find that it does it more often after a hard pull through the gears or right after a cold start when I pull up to the closest light (Car warmed up of course).

If you were talking on behalf of the previous owner, then the problem still remains and is yet to be solved.

 

[97moneyhole]

I am also running into this same problem. At idle my A/F is reading between 15.9 and 16.4 and i have not changed my afc settings at idle (-3) .During crusing speeds it is perfect (14.4-14.7). At WOT it stays right at 11.1. I believe that i have a boost leak because my vac is only reading 12 inHg but then again i just moved to laramie (7200 ft above sea level) and it holds at 20psi.

 

[sirsol66]

Wow, good to know that other people are also having this problem. I have a fairly stock (bolt ons only) 98 gst and it has done it since the second week I have owned it. If anyone ever figures out what the problem is, please pm me.

 

[97gstjosh]

Just chimming in. Mar car has the same problem. It started ever since it got cold out like 40 and below in the morning. It starts a little rough and then goes extremely lean. my turbo timer goes up to like 19.x something and almost stalls out then goes to the 14.7 range then goes back up and does that for about 2-3 mins then its fine for the rest of the day. Im going to blame it on the cold along with all my mods. I dont have this problem in the summer time at all. Anyone have any ideas yet besides the weather and your mods?

 

[BoostFrenzy]

Anyone have any ideas yet besides the weather and your mods?

I originally only had it on cold days too. But now it is every time I clutch in almost. It's not too bad anymore though. It is only really bad when I try and give it a little gas to keep it going and it just bogs from no fuel.

I have narrowed it down to either being something wrong with the MAS or something with how an AFC messes with the MAS. I'm installing DSMLink in my car soon and once I do a FMIC I am going to go with a GM MAF as well. So over time, both of my theories will be tested.

 

[97gstjosh]

I have an auto so I dont have to worry about the clutch. I have DSMlink installed and I have this problem. I will know when it warms up if it keeps doing it. Im switching over to MAFT soon too so we will have to see what happens. It just drives me insane.

 

[KnightHawk434th]

Not trying to highjack this thread or bring up an old message, but my car is having the exact same problem. I have a 99 RS with EGR blocked off, CAI, ebay header/muffler (soon a whole catback), DXD clutch and ebay cam gears. When I clutch in to coast up to a stop it idles at 1200, but soon as i come to complete stop it bogs to 850-900 and surges like crazy (this is only after it has warmed up). Another thing I noticed once this arised was that between 5000-6000 RPMs the power seems to fall off the face of the earth. I checked my plugs thinking they might be fouled, but they look a little lean. I mean they are a really light gray and show no signs of even firing or being exposed to fuel, but yet my car runs perfect once I get moving again.

I've read it could be a timing issue, a cam/crank sensor (cam sensor is brand new), the IAC motor (last checked since my build, there was nothing abnormal about it...no gunk build up, but the motor seemed to move to easily), a coolant sensor problem, thermostat (also heard that you should be able to squeeze the upper radiator hose...it's like squeezing a rock, problem?), spark plug wires or even a fuel shortage problem. I began to think of possibly being not enough compression due to maybe an accidentally aligned compression ring set during my last build, but haven't had the money or the time to do a compression test. I talked to some people, and they think my header might be causing a problem with tricking the ECU into not seeing enough backpressure to stay running correctly, but that doesn't make sense since too many guys have thrown a header on and were fine. I just started noticing this since it has been cold outside (average temp is around 25*, but i didn't have this problem last year).

Anyone have any light to shed on the problems this might be? BTW, did anyone ever get this problem fixed on their car? If so what was it?

 

[xdxoxuxgx]

Has anyone resolved any of these issues yet, I'm curious because my car appears to be having the same problems. It's fine just driving through town, stop light to stop light, but when I get on the highway and stay at a constant speed/rpm for a while the wideband will eventually drop to lean off the charts. If I push the gas in all the way then it will read richer but if I just push the gas in a little bit the wideband will go up to maybe 13 then will drop down to lean off the charts again, and will idle like hell when I roll to a stop. After it sits and idles for about 30 seconds, with the help of me tapping the gas pedal every now and then, the rpms will jump up and return to normal idle and it will drive fine again. If anyone could shed some light on this, that would be great.

 

[turbotsi90]

mine is also doing this, when I started my car from cold it idles awesome, then after what seems to only be a minute or less it starts idling rough and my WB is reading very lean. Also when shifting between gears it reads very lean

any help would be much appreciated

 

[super97gst]

Most of these types of problems that originate depending on the outside air temperature are usually caused by the MAS. The MAS contains 2 different sensors: intake temperature sensor and the barometric pressure sensor. When one of these 2 sensors starts throwing fits the engine will have idle issues fluctuating depending on the ambient air temp. Try testing your MAS and see what you've got. Neither of the sensors contained in the MAS are changeable. The entire MAS has to be swapped.