Slightly different high idle issue?
Thread Starter
Intermediate
Joined: Feb 2006
Posts: 28
Likes: 0
From: Eldersburg Maryland
Slightly different high idle issue?
Hi,
I have a stock 90 L98 with 24K miles on it. The idle on it was getting rough, surged sometimes, idle'd real low, idle'd real high, etc. So, I took the TB off and totally cleaned it out, replaced all the gaskets, etc. I purchased a new IAC valve as well. Put everything back together. It idles a little better...a little better "consistent" idle now. However, there will still be times where the idle is fine...I drive it on the highway for a while (> 15min) and I pull up to a light. The idle will be racing at about 1500rpm. It will stay that way for about 30 sec and then start to migrate down to the expected 600-700rpm. After reading all the other high idle comments, my thoughts are..
1) Don't think it has anything to do with the TB not closing all the way...else I don't think it would ever migrate back down to 600-700rpm.
2) Don't think it is a vacuum leak issue...
3) I'm thinking it could be an ECM issue?
4) I'm thinking it could be a speed sensor issue?
Any other ideas and what to do? Thanks!
I have a stock 90 L98 with 24K miles on it. The idle on it was getting rough, surged sometimes, idle'd real low, idle'd real high, etc. So, I took the TB off and totally cleaned it out, replaced all the gaskets, etc. I purchased a new IAC valve as well. Put everything back together. It idles a little better...a little better "consistent" idle now. However, there will still be times where the idle is fine...I drive it on the highway for a while (> 15min) and I pull up to a light. The idle will be racing at about 1500rpm. It will stay that way for about 30 sec and then start to migrate down to the expected 600-700rpm. After reading all the other high idle comments, my thoughts are..
1) Don't think it has anything to do with the TB not closing all the way...else I don't think it would ever migrate back down to 600-700rpm.
2) Don't think it is a vacuum leak issue...
3) I'm thinking it could be an ECM issue?
4) I'm thinking it could be a speed sensor issue?
Any other ideas and what to do? Thanks!
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
That's exactly what my 85 is doing. I also cleaned the TB and replaced the IAC with no change. I adjusted the TPS and verified no vacuum leaks. I don't think its a binding cable because I verified the throttle blade is closed. Like you, I think its a sensor issue but I don't know what all the ECM looks at to determine idle.
Thread Starter
Intermediate
Joined: Feb 2006
Posts: 28
Likes: 0
From: Eldersburg Maryland
Any recommendation on a scan tool that does this stuff...? ...or does it have to be a fancy one at an INDY shop? Can I just get one for $100-$200 that does both OBD-1 and OBD-2?....I have heard of Auto X-ray....and Actron....
Melting Slicks
Joined: Mar 2008
Posts: 2,141
Likes: 76
From: Santa Maria, CA
I just ordered an Auto X-Ray 3000 on eBay. Its supposed to read all the values in the ECM. Cost was $89.95 + shipping. The cost is right because it's a discontinued model. Hope it works.
