Cars a 90 tbi. Autp trans. About 250k on motor. Head was replaced at 100k. Trans at 150. Issues i have are, rough idle. If i turn on the heat sometimes the car stalls but fires right back up and others it almost stall but recovers. On cold start it fires off 100% easy but as its running high idle and coming down it starts sputtering a bit and settles the rpm but still misses a bit here and there. Driving wise is ok. Plenty of power. Sometimes if u drive it then put it in park it will idle and then after a few seconds it will start reving up and down. Also sometimes turning on the headlights will make it almost stall. I swaped the intake over to a mpfi setup. Changed fuel pump. Old tbi was getting worn out. Same issues are still there. If anything ita gotten worse. Ive checked vac lines and replaced a few. Also did idle relearn. I do have access to a scanner. Any ideas or what to look for? Maps relatively new and so is o2. Coolant sensor is ok and so is intake air.

It could be the IAC is gummed up or done for.I would also check your EGR valve for carbon build up and as the egr valve's vary on design (if it is loosing vacumm) it could be going bad.I could say the typical things like coil packs or plugs,pcv valve but I doubt these are the issue.A simple check on the EGR is disconnect the vacuum line and try driving and running it as normal.IF this corrects the issue try cleaning the pintal area of the egr and reinstall.Then reattached the vac line and .If this after cleaning makes 0 difference it could be the diaphragm is cracked and leaking air(vacuum) and needs to be replaced.I am leaning more towards the IAC valve or egr and not the typical tune up items.Granted I could be incorrect on my diagnostics and unless you repost this over in the 2nd forum where some more fluent 2nd guys check in can better address or add to my thoughts.I do not think your TCC switch on the trans is a factor either as typically this is relevant when the car is IN a gear not park.1 more if it were the TPS your throttle would be all over,dead spot and or hit and miss while driving,parked or revving .I got carried away with idea's.Do the IAC and egr checks.

i was doing some research and found a guy with almost the same issues. so i looked into mine, it looks like the fuel regulator is frozen in place and holding the pressure high. the intake was off a car in the junkyard but only had 75k on it. so then he also had a leaking fuel injector. so i tested mine and it looks like i might have one as well. tomorrow i should be able to replace the regulator. then im gonna test the injectors again.

I got it on the scanner. I replaced the o2 as well. What i noticed was the tps signal. As i pushed the gas the voltage changed but % of throttle did not until i was about 10%. Also when i floor it, it doesnt read 5 volts and it doesn't show 100% throttle. Any ideas on why this is? I took it to my shop and they have no ideas as well.

http://www.wellsve.com/counterpoint_issues97-00.html Go to this site and then click on the Volume 2 1998 issue 1.I do not want to kick on your shop but, this is really elementary.Basically with a multimeter set to OHMS (20k) you rotate the throttle with the KEY ON engine not running.What you want is a Smooth gradual upgrade to wide open throttle.The tps in terms of voltage should go from as little as 1 volt to no higher than 5 working correct.In my opinion you have a defective TPS sensor and it will NOT necessarily kick a CEL as this is to small in increment's for the ECM to register the fault.I will say in the OHMS position move the throttle up lightly and you should see the numbers go up nice and SMOOTH meaning up gradually and not a hesitating or drag or stop and then move period.IF your car shows this on the ohms your TPS is well worn out.Replace it and you will have to do a relearn to get this adjusted.Remove old part, install new and turn key on and then apply the fuel pedal from idle to wide open gradual and wait a minute.Then crank the car and see if the New part adjust correct..Now I may have to revise the relearn ordeal but the ecm does have to calibrate the new tps and just a swap and crank will not fix the issue.I strongly suggest saving the site I shared as this site can school you in the checking of many sensors and easy to use!! I will dig into the replacement side as I am a little bit rusty but,understand the diagnostics side very well.I think your TPS has a dead spot as based on your information that is what is happening.

Skip the relearn I was thinking IAC.Just replace the TPS and turn the key on (I personally still would wait a minute) and then crank and it should run fine in my thoughts.Over thinking I was.

I looked inside the tps adjustment test on the scanner and its within range. I wouldve thought powering down ecm it would relearn. I know the adjustment screen says its a non adjustable tps.

Update for today. What ever it is, its getting worse. Now im having issues that if its hot it wont start on the first try and has a hard time on the 2nd but does fire. Almost sounds lime its flooding out. It started fine this morning but after work it was hard to start as well. I unplugged the o2 and didnt seem to improve anything. Another thing i noticed is if i punch it, it almost dies and then recovers. If i keep hitting the throttle and releaseing it quickly after a few times it will die. Hooked up the scanner and everything is ok. One thing i noticed is if the engine is running tps works fine so that's not it. I alao held the throttle at 2k and you can hear slight poping in the exhaust and you can feel it in the motor as well. I checked fuel pressure reg and its not leaking.

Ok time for the maybe silly question that is not really silly.How old is your cat convertor and your muffler.Reason I ask it seems you have a restricted exhaust system which in turn can exibit your exact problem based on my real experience on other cars.As the engine and exhaust get hot it reduces air flow out the tail pipe.Only way to know it cut off or drill some big holes in the pipe before the cat (ones that can be patched back) and see if it reduces the problem.I know drilling holes is like (what) but either that or cut off the cat and run straight pipe temporarily if your exhaust is over ten years old or more.That is my quick thought.

I know the cat was replaced before but it was some time ago. I dont think the cat would cause a hard start issue though. Also car has tons of power when driving. I may still pull it off though and try what you said. The muffler is aftermarket so i know thats good. Then this morning i started it and started right up. No issues other then its normal idleing issues. Yesterday when i started it after work it was about 80 out. This morning it was about 55 so im thinking its gotta be something temperature related. Im starting to lean towards maybe the ignition module or coils. I know module was replaced years ago at least 10. Coils were changed 5 years ago but were used. I dont think the cps has ever been changed. Anything i should look for?

Coils are def a heat related part.I am slightly tired tonight and will ponder the thoughts will working sat driving the tractor trailer and will think it over some when not well tired.