NiteStar

I've been having this problem for over a year now. For the first year it would all of a sudden start to IDLE high while driving and sometimes come back down to normal or other times I would shut the car off and it would maybe fix it. It also seemed to start up @ higher RPMs than normal. Just in the past 4 months it's now started to start up @ only 700 RPMS even when sitting for over 1 day. I also noticed that when it starts @ 700 RPM's it will drop to 300 and then go back up to 700. When it's acting up like that it will go down to 300-400 RPM's when i'm coming to a stop and then go back to 550. It's stalled on me about 3 times already. I've replaced everything I can think of. Spark plugs/cap/rotor/ICM/coil/TPS/IAC/MAP/IAT/EGR. I believe the high idle and low idle are related. Mabye it's the problem getting worse. I don't know. The problems, whether it's the high idle or low idle, will not happen all the time. Any ideas would be very helpful. Thanks.

onfire

Nitestar,

Have you set the correct voltage on the tps to .45
I think thats right. Hope someone will back me up on this.
Have you done any modifications to your motor?

You pretty much have the same motor/trans/rear gear as i did when i first got my ride !

Check for any vacuum leaks and make sure your timing is at 6 if your setup is still relatively stock. Again thats 6 with the esp wire unplugged (its the tan wire up towards the passenger side closer towards your firewall).

Happy Hunting!

Rabi C>

NiteStar

.45? I thought all I had to do was swap parts out. Still had the same problem though after changing the TPS (the high/surging idle). I think (hope) the low idle problem is the problem getting worse. I've sprayed some carb cleaner on some vacuume line around the plenum and didn't notice a change in idle. As far as the timing being off, would that cause intermittent idle problems? I'm think that if it was off, I would have the problem all the time. Let me know please.

InterceptorZ28

I have had the same problem, and your voltage on your tps is i thought between .6 and .9 because it should be auto zeroing. that only applies to 90-92 motors i believe, yours should be automatic, mine is and it's a 91. as long as you don't have a check engine light on, your ok. as far a the bouncy idle, mine has been doing that for a while as well, and i replaced all the sensors too. everyone kept telling me it was the tps or iac, but it kept doing it. mine stoped when i took the throttle body itself apart, and cleaned it real well. Try that and see what happens, I know mine doesn't bounce the idle anymore.

NiteStar

I'll take my throttle body apart tomorrow and see. I might add that there have been a few times I had to give it gas when starting to get/keep it running on start up, but only at start up and not after.

rgarcia63

If the TPS is auto ranging then be sure not to step on the gas pedal while turning the key, this will cause the ECM to zero the TPS at a higher voltage than normal.

NiteStar

I looked at my throttle body and noticed that the area that gets the air through for the IAC valve has my TPS air-splitter in front of it with a hole at the bottome for air to get in. I wonder if it's dirty behind that and that's my problem. I'll take it off later and find out. What do yunz think?

NiteStar

Just got done cleaning out the throttle body. Used 2 can's of carb cleaner. lol. When I first started it up, it went up to 1700 rpm's and came down to about 850. I realized I never disconnected the battery, so I went ahead and did that. Then started it up and it seemed to act normal. I can't tell yet if my problem has been fixed. My question to yunz is.... when you're doing 45-55 mph and put the car in nuetral, should it go to 700 rpm's? Mine seemed to want to go only as low as 950-1000. Also when you're in sitting still in drive and you're rpm's are 550 and you put it in park, should the rpm's go up to 700 or go up to 800 and then come down to 700? I can't remember anymore what normal was.

NiteStar

nm. I kind of answered my own questions there. When it's not acting up it'll drop to 7-800 rpms in neutral even at 50MPH. Maybe it's a vacuum line i missed but i just don't know. I'll I would like to know what the normal start up idle is supposed to be (like it rev's to 1500rpms and then comes down right away to whatever). Can a vacuum line create intermitten idle surges that last for whole drives and then other times act normal? If anyone knows. As for me, I guess, let the hunting for that vacuum line begin.

strider681

I am experiencing somewhat similar problems.. started like this: when starting up cold, idle bogged so low i had to press accelerator so it wouldn't die until it warmed up a little.. then idled pretty much normal after that. so I did like most ppl here and sprayed a bunch of carb cleaner in my intake. Then my car started idleing really high (1500-1800 RPM's) went i put it into park after driving (warm). I replaced the IAC valve and further cleaned out the throttle body. After making sure min idle was set right and resetting the computer it ran fine and idled normal. After driving a few times the extremely high idle came back. Sometimes it only idles a little high about 800-900 RPM's. As far as I know normal idle conditions should be: when starting cold idle surges to about 1200 RPM then gradually comes down based off temp. when warm idle should be about 600 in drive and slightly higher in park. I noticed my TPS voltage readings being a little off, when opening the throttle it drops down to 0.005 and other lower than normal values so this may be my culprit. I also need to replace all my vacuum lines anyways, they are cheap enough! well hope some of this might help you with your problem. Good Luck!

NiteStar

Yep strider681, problems do sound similar. If you figure out what the problem is, would you please let me know. I'll do the same as well. btw I thought the high idle and the low idle were the same problem, but I took my throttle body completly off and used like 2 cans of carb cleaner on it. It's been a week and the low idle hasn't come back. (knock on wood). But the high idle is still as bad as ever. Doesn't matter if cold start or not, when I start it up it goes up to 1500-1900 RMS's and comes down to idle. And like yours, it'll idle in drive at about 800 and in drive 1050 at times. I plan on doing my vacuum lines later this week. It's the only other think I can think of that could be the problem. I'm told my TPS is auto ranging, so I don't think it's that. Besides I actually have bought 2 since the problem started. I don't think all 3 could be bad. Again, please let me know if you figure out what your problem is. Thanks.

strider681

well my porblem finally went away! (knock on wood) i'm not sure exactly what I did different this time but basically I did the TPS and IAC adjustment procedure listed in the Tech Articles, adjusted min idle to 450 RPM in Drive warm, and checked timing to 6 degrees BTDC. one thing I did too was sprayed some carb cleaner on my TPS but it still reads wierd values (0.005) but my car idles normal now. the thing I think that made a difference was I have my idle set screw backed way down now. I turned it at least 3 or 4 full turns back from where I had it previously. make sure you jumper A & B on the ALDL for at least 30 seconds and unplug the IAC connector while it's jumpered. turn off ignition and remove jumper. start engine and adjust min idle to 450 RPM in Drive (NOT in park) when warm (195 Degrees). if you don't have a scan tool it'll be hard to tell when it's around 450 RPM so basically right before the engine dies is about that. well hope this helps with your problem, and I hope mine stays gone! Good Luck!

strider681

oh I forgot to add that after setting the min idle and you hook back up the connector to the IAC, you should pull the ECM fuse comming off the positive bat cable and wait a min or so b4 putting it back in. per the chilton manual you should then start the engine and let it run 5 seconds. turn off engine for 10 sec. after that it should idle better after you drive it at least 30 min.. oh and I have my TPS set to .54 while engine running. I don't know if it's wierd or not but my TPS reading is .02 less when engine off ignition on. one way to check if it's the IAC or not is to jumper A & B on the ALDL for 30 seconds and disconnect the IAC. turn off ignition, remove jumper and set min idle to 6-700 RPM. I was able to drive to and from work like that with out the high idle so I knew it was something to do with my IAC. I thought my TPS was causing it from reading this and other threads, but it seems now like for me at least it was my min idle set screw being too high.

rgarcia63

Please post an update in a few days, I seen this come back on other members. It would help to know it is stable.

strider681

so unfortunately not only did my problem come back, but it's worse! I got the high idle and then it finally threw a code, TPS voltage low. so I replaced both the connector and the TPS and I thougt I was finally done with it. not so, after almost a week of no code and no high idle, it went right back to throwing the same code but the idle doesn't go as high. I checked the ground and VCC at the connector, ground was solid but the supply voltage was only 4.93. in the wiring schematic it shows the TPS shares ground with coolant temp and intake air temp sensors. I checked out the coolant but the intake it harder to get to. not sure if it's related at all but my top gear engaged keeps going from engaged to not engaged sporadically, even with key on engine off!? I'm just hoping my ECM isn't taking a dump after 20 years well once I find out what's causing my code for low TPS I will follow up on here.
and a note to NiteStar, yes you do have to set the TPS to a certain voltage range between 0.47 - 0.62, with .54 being the center of that range. I have an Auto XRay scan tool to read that, if you don't have one you have to use jumper wires on the connector, a real pain.

NiteStar

Thanks for the update strider. I've kind of taken a break from figuring out what it could be. I'll start trouble shooting again soon. I did want to bounce one idea off yunz. Could a bad charging system (alternator,battery, or both) cause the intermittent High idle? Just a thought. Let me know guys. Later.

Camaero

iTrader: (2)

Any updates to this? I am sort of having the same issues...

NiteStar

No updates on this from my end Camaero. I'm thinking my problem is a vacuum leak. Just haven't had the time to check yet. If you haven't tried looking for a leak already, you should try that first. I'll update here if I find a leak and if it's the problem.

thunder85

iTrader: (1)

just out of curiousity, has anyone monitored the supply voltage to the sensors to see if there is a variance? replacing the sensors over and over, and still having the same results makes me wonder. i have seen one or two cases where the supply voltage fluctuates and causes all sensor values to skew, thusly causing an issue with the idle values and map/maf sensor values.

NiteStar

Better late than never, right? Sorry. I hope this helps out others in the future.

As you can tell from my first post about 4 years ago, one of the problems I had was a fluctuating High idle. I had this problem off and on, but always daily. I had replaced the TPS sensor and it still did it, so I of course moved on to other things. Well after 3 1/2 years the problem got really bad. I mean for the most part, every few weeks I'd have an instance where the car would start to miss and jump when stepping on the gas pedal and it would just "go away" after turning the car off and restarting. That I could live with or rather, forced myself to live with. Well running at a high idle in the summer time is bad enough, but it actually started cutting my throttle off at the beginning of summer I mean, when I'd pull out into traffic, I would be on the gas pedal and then it would just stop going completly. I had to drift to a stop one time and re-start the car to get it going. Well I didn't mess around with that. I decided to go ahead and replace the TPS again and wouldn't you know it, that problem and all the problems of High idle of the last 3 1/2 years are all gone. It's been 6 months now and it's been 100% ok.

So I can only assume that the TPS I bought 4 years ago was faulty out of the box. I hope this info may be of some use to future owners of firebirds/camaros with similar problems.