minor low erratic idle during warmup

[cncmachinist2]

I've recently had an idling issue. At first it was idling high around 2000 consistantly w/o any service engine light. I jumped the dlc myself because i have obd1 and no codes. I took it upon myself to guess and check by replacing the IAC valve and it fixed the problem. I did that saturday the 9th, and up until today the 11th it was fine. Idled fine during warmup, and driving. This morning when i was going to work I had a problem with it starting. Everything was working but it just didn't want to completely turn over. It doesnt even keep trying to turn over with the key still pushed forward, it stalls after a couple seconds. I tried a regular start twice, no difference. I then applied a little bit of gas during the third attempt and it turned over fine. It however idled low, sorta like a cold start, but it stayed low even when it warmed up. the rpm's at 800 but it sounds lower and it is erratic in that it fluctuated between 600-800 about 3 times. And when I apply gas while idling, when it drops back down to normal idle speed it again bobs a few times between 600-800rpms and when doing so it feels likes its going to stall. Lights dim, fans sound like theyre going too, but it doesnt and its only for a quick sec during the fluctuation, then it stays around 800 rpm and idles fine, still low but fine. It does that everytime i apply gas. The drivability is excellent though. No changes in acceleration or deceleration, no erratic idle at stops or while driving. I even think it drives better than before the IAC went kaput. In fact I know it does. When I got out of work this same day, i had the same problem starting it again. only this time it didnt stall after 1-2 seconds of having the key still turned and it trying to turn over. It did it like 3-4 seconds into the first attempt. And then again in the second attempt. On the third attempt I applied a bit of gas, and it turned fine. Also when i apply the gas i dont gun it or hold it down, i barely tap it and as soon as i do that i let the key go (so i dont screw up the starter) and its fine again. It also idled the same way as described above, only this time the electronics didn't show or sound like they were going to stall.

The service engine light does not come on. I haven't tried getting the codes yet. A buddy of mine at work told me that it may be the computer trying to relearn since I put in a new IAC valve, which i do understand this concept, but i dont see why 2 days after the fix it is now 'learning'. Also do note that on the friday before the day i fixed this initial problem i did clean out the throttle plate with intake/throttle cleaner and a toothbrush first. Also my voltage guage stays consistant around 13, and the oil pressure guage stays around 60 during idle like normal and neither doesn't fluctuate with the rpms during the erratic idle. or so i haven't noticed. I did pay attention to those gauges so if i am wrong, then they are not moving very much to be noticed.

I do not know what the problem is but i do have some ideas. I think im going to replace the MAP sensor and see if that helps, but i dont want to do that if it isn't anywhere near the solution.

[lozanoa11]

it will take a while to re learn. the problem with obd1 was it never sets codes or it sets false codes

[MP81]

Coulda been the insane cold too...

[cncmachinist2]

Yeah, i think its the cold. tonight after work i had the same trouble starting it and this time i had to idle the engine applying gas for about 2 minutes to let it warm up enough to idle on its own without stalling. once it warmed up no problem. and when i stopped at a gas station, it started fine on the first and only attempt when i left. so far as i can tell there are no vacuum leaks...yet. I'm going to check my fluids in the morning. Might be low on antifreeze or something.

[cncmachinist2]

more trouble. still idling low during warmup and now during driving. when i come to a stop or slow down, or drive slow like in a parking lot it idles low and wants to die. Mainly right after letting off the accelerator. i think its the fuel pump. I dont know exactly what but it definetly has something to do with it. Im going to have it looked at for voltage. maybe why its not starting correctly and everything dims when it pumps gas on its own like during idle or controlling the drop in pressure when letting off the accelerator. I find i dont have this problem if i let off easy controlling the idle speed, where as if i dump it and let go it drops just as fast and instead of controlling the drop in speed it just drops and sometimes to fast for the pump to act and flow fuel into the motor before it bottoms out and eventually dies.

[ITSSLOW]

Brenna's 3.4 'maro did that a few times when I drove it when it was like -10 out earlier this week. Once I instantly let off the throttle it really started surging and wanted to die so I'd give it alittle gas and then it would return to idle normal. Never done it before and hasn't done it since it got back into the 20's. I just blame it on the extremely cold weather we had earlier this week and last weekend.

[JoeliusZ28]

this is pretty basic, but have you cleaned the throttle body lately? They can get pretty gummed up and sticky after a while... it takes a little more than a shot of carb cleaner to get em clean again.

[cncmachinist2]

A buddy of mine at work told me that it may be the computer trying to relearn since I put in a new IAC valve, which i do understand this concept, but i dont see why 2 days after the fix it is now 'learning'. Also do note that on the friday before the day i fixed this initial problem i did clean out the throttle plate with intake/throttle cleaner and a toothbrush first. .

I thought it might be the cold weather too as it started when we had the extremely cold weather earlier this week too. but these last two days have been warmer compared to monday and it still doing it. although i do not have to idle it myself with the pedal during warmup nearly as long as did tuesday when we had that storm, but i still have to do that and its behaving like its not going to get better than this. maybe the initial problem with the high idle before changing the IAC caused the fuel pump to screw up when it was overworked. I think thats why it is sucking up power when it pumps on its own. I don't think its broke, maybe something electrical with it is. thats why im taking it to have the voltage on it checked.

[MP81]

You said everything dims when the car goes to die?

Alternator...?

[cncmachinist2]

yeah, but i mean the lights kinda flicker and the motor stutters together in harmony so to speak and thats only when the idle drops to about 400-500. If it were the alternator it wouldv'e died on me by now i think. I've had this problem for about a week now and the car's behavior is unchanged. it hasn't got any better but not any worse either...so far. The only difference is when it gets really cold i have to idle it with the pedal for about a minute to get the fluids in it going and get the motor warmed up enough to idle itself.

I went to autozone yesterday to talk to a tech. I explained everything to her and she said that it's not the fuel pump because it still preforms at all speeds when i apply gas. (I even took it on the highway for a quick sprint to see if there was anything wrong that i havent come across due with high speeds. the car accelerated at normal speed and didn't let up. it drove like there was nothing wrong.) She says it's one of 3 things. First she said it probably is the MAP sensor, may have been the problem to begin with. It may be going bad getting incorrect readings allowing the computer to adjust the fuel to air mixture to a lean ratio due to high air pressure readings it thinks its getting. Or it could be the coolant temperature sensor going bad reading incorrect temps allowing again the computer to adjust the fuel to air mixture accordingly and may be why it behaves different in different temps. But she also said that if I am unable to get the obd1 codes off of jumping it may be a wiring issue somewhere. I should atleast get a code 12 even if theres nothing wrong and i dont even get that. The ses light does come on but it don't blink. She thinks there might be a problem in the wiring, like an exposed or corroded wire somewhere or something grounding out or crossing not allowing proper communication between the computer and any of the sensors, primarily the two afformentioned. So I have no choice but to take it to get a full diag to get a live reading. I could replace those two sensors for about the same price as a diag but if it is a wiring problem it could be a worthless guess and check.

[1BADAIR]

check the coolant temp sensor with scan tool. Does it smell rich?

[cncmachinist2]

im getting the diag done tues morning. Using a scan tool is not going to help because i cant get any codes to begin with by jumping the dcl, not even code 12 comes up. It doesn't smell rich to me. when I did have the prev high idle problem i could tell it was running rich by smell, but not now. If it is running rich, it's not enough to smell it. I actually think its running lean given the circumstances. I also noticed, tonight it started and ran like it has been, even in the sudden drop in temp from yesterday.

[cncmachinist2]

well the shop called me back today. appearantly there was a minor vacuum leak. One of the valves was in bad shape and they're waiting on the part to replace it. they found it by having the car run and then systematically pulling out valves and replacing them one by one. they did not say however which one it was, even after i asked. they haven't put it on a diag yet, they want to wait to fix this first. they say it should be fixed tomorrow, which will then allow them to run a diagnostic to check the electrical problem. they said eventhough this may fix the starting and eratic idle problem, it does not address the problem with the obd no code. it explains however the ses light not coming on as it was a small enough leak that the ecm was 'correcting' it by adjusting the fuel air mix as needed and not throwing a code, although it still should have put up a code 12 when scanned. fixing this first will eliminate it as a possible problem on the diag allowing them to narrow down possibilities in the case that an obvious problem doesn't appear for the electrical problem.

[cncmachinist2]

well, it took a few more days then expected but it is fixed. it ended up being the coolant temp sensor. they replaced it for free because they did not get it right the first time when they replaced the IAC that I replaced. They were even nice enough to deliver it to my house when it was done. so far it has been running like normal and starts fine. Hopefully this is the end of this problem.