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High idle - 2K, then 1.5K 87 GT 5 Speed by jasonn674
Started on: 10-29-2014 03:59 PM
Replies: 2 (77 views)
Last post by: jasonn674 on 10-29-2014 04:21 PM
jasonn674
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Report this Post10-29-2014 03:59 PM Click Here to See the Profile for jasonn674Click Here to Email jasonn674Send a Private Message to jasonn674Edit/Delete MessageReply w/QuoteDirect Link to This Post
‘87 GT 5 Speed 79K miles. Just bought it a month or two ago. The car was sitting in a barn for 8years or so.. Needed a fuel pump and then it started right up. (at that time it idled fine at 900rpm)

So, the other day I decided to spray some Mopar combustion chamber cleaner in to the throttle body..I was really liberal with it and even sprayed in to the IACV hole, wasn’t sure that was such a good idea or not... There after, it started to idle high..around 2-2.5K and when warmed up.. 2K then drops to 1.5K after like 5-10sec.

On my journey to discover what the issue is and where...I first figured it’s probably a vacuum leak somewhere, checked around some (prolly not enough) I couldn’t find any leaks. So I decided to replace things.. I wanted to anyways.

Things I’ve done so far to no avail:

- Unplugged the EGR valve vacuum line and tested it to the solenoid. The egr valve and line to/from solenoid seemed to hold the vacuum under it’s own pressure by pushing up on the egr diaphragm.
- Blocked off EGR tube, to see if it was cracked somewhere. Didn’t make a change in idle.
- Unplugged the vacuum line under the throttle body going to the EGR solenoid and plugged it off on the end of the TB.
- Replaced the IACV and reset it.
- Put my thumb on the hole in the TB covering the IACV..lowered idle to about 1K or so but did not stall.
- Replaced the vacuum lines around the cruise control and checked all the lines to the vapor filter next to the air cleaner.
- Sprayed throttle body cleaner on most all of the vacuum lines and around throttle Body. Didn’t seem to change the idle? I stayed clear of the sensors...
- Sub-note, before the high idle, I also replaced the pick-up coil, coil, and ICM. Pick-up coil was shot.

I have NOT re-timed the car after pulling the distributor, but it’s really close I think. Aside from the high idle it runs great and doesn't backfire or miss.

Any helpful thoughts on this? Could the timing cause such a high idle?

Gosh, do I need to pull the Throttle body out and check the other vacuum lines? Maybe it’s the o-ring near the IACV going from the TB to the lower manifold?

What else could cause this high idle?

Thanks! Jason
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Gall757
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Report this Post10-29-2014 04:09 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
There is another short vacuum tube under the throttle body that you probably dislodged. It's a larger diameter...about 1/2"....
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jasonn674
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Report this Post10-29-2014 04:21 PM Click Here to See the Profile for jasonn674Click Here to Email jasonn674Send a Private Message to jasonn674Edit/Delete MessageReply w/QuoteDirect Link to This Post
Was kinda thinking that too. I'll look again, but last I looked I thought it was ok.
I believe that's the tube which goes from the IACV to the lower intake manifold. As I understand it there is also an o-ring in there which is said to go bad.
I guess the only way to really see in there is to pull the distributor out again and check?
hope that's it.. smaller tube vacuum leaks wouldn't make the idle that high, would they?
But that large 1/2" tube would definitely make a very high idle lol.
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