Engine fast idle
Thread Starter
On The Tree
Joined: Jun 2003
Posts: 186
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From: Illinois
Engine fast idle I have a 98 z28 and it has a fast idle problem i cant seem to get fixed. I have done everything i can think of and it still is an issue. I will get in it and start it and it may idle fine for a minute or two and then all the sudden its like you put your foot on the accelerator and it revs up to 3000+ rpm and wont back down for anything. If i shut it off it will then rev right back up when i restart it. If i take the battery loose and rehook it back up it sometimes will then idle back down to normal on the next start up but it only lasts for less than a minute then goes crazy again. Anyone have any ideas where to go next with it.
Thank you
Thank you
I have a 98 z28 and it has a fast idle problem i cant seem to get fixed. I have done everything i can think of and it still is an issue. I will get in it and start it and it may idle fine for a minute or two and then all the sudden its like you put your foot on the accelerator and it revs up to 3000+ rpm and wont back down for anything. If i shut it off it will then rev right back up when i restart it. If i take the battery loose and rehook it back up it sometimes will then idle back down to normal on the next start up but it only lasts for less than a minute then goes crazy again. Anyone have any ideas where to go next with it.
Thank you
Thank you
You could do what I do with sensors and valves and little **** parts like that.....just go buy a new one real quick, pop it in and see if you're good to go. If not......clean it and return it in a few days, just tell them it was the wrong part and you NEVER EVEN installed it.
Then.....start looking for the vacuum leak....because if the IAC valve is good.....the ONLY thing that can INCREASE rpm's is MORE air getting in somehow. There is no other way an engine can rev UP. Air only.
But, if it were a vacuum leak it should shoot UP in rpm's the second you start it, not after one minute. Vacuum leaks are there or they are not there. And yes, sometimes they do show themselves AFTER the engine is warm and seals/gaskets/plastic can get soft and then the vacuum leaks can start. But they are not just BAM....3,000 rpm. They will be all erratic and different each time they start to leak.
I'm thinking since it happens when you hit the throttle, and it always goes up to 3,000..........IAC valve.
But with that said......it can still be 10 other damn things.......lol....
---could also be a worn TPS that's telling the PCM wrong info, causing the PCM to open the IAC valve. That has happened to my car years ago. So maybe after trying the IAC valve, try a new TPS. Again.....return them if they don't fix the issue. Free diagnosis......
.
look and make sure the throttle body blade is closing all the way, start the car and touch the throttle bracket and see if it is closed all the way when it should be at idle....
i would also look for a vac leak
i would also look for a vac leak
It's electrical, I've seen it before. Since it stops when you disconnect the battery, the pcm resets.... different things help different people... tps sometimes works. Usually iac is ok, since it's being told to open and does so....
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Thread Starter
On The Tree
Joined: Jun 2003
Posts: 186
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From: Illinois
Thank you for the ideas on things to try thoughi really appreciate them.
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On The Tree
Joined: Jun 2003
Posts: 186
Likes: 1
From: Illinois
1 car I tried was tps... My car, still no luck. Happens every 3-4 months and I shut the car off with my kill switch, start back up and she runs fine.... For me it's not a big deal, have not investigated further... But the root problem is your IAC opens all the way. Causing high idle. If you use a scan tool and close the iac, it will return to normal idle. Therefore, no vac leak. it's being commanded to open.
Thread Starter
On The Tree
Joined: Jun 2003
Posts: 186
Likes: 1
From: Illinois
OK.just yet another update. I switched out to a completely different throttle body and. MAF. the car ran well for about 30 minutes then it started to idle about 3000 rpm again. When it did it it Sounds like a massive vacuum leak. Help........
