89 Bonneville, Motor jumping problem - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-12-2006, 03:50 AM   #1
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Default 89 Bonneville, Motor jumping problem

1989 Pontiac Bonneville LE V6 3.8L AT

I got some screwed up problems with a car again, I'm starting to hate Pontiac. When shifting between drive and reverse, or netural to reverse, the engine kicks like someone slams into the car. Every single motor/transmission mount had to be replaced because they all broke at once, and it'* not long till it happens again. Also the electronic ildler control valve had been replaced. From what I can make out of it is that it seems like the car is to rev'ed up and that'* why it kicks when shifting. The engine even sounds a lot louder like someone has their foot on the gas. Is there anyway to adjust anything, the cable for the gas or an adjustment on the ildler?

Thanks for any help.
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Old 10-12-2006, 10:29 AM   #2
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This car should Learn the IAC position once the car is up to temp and you are going over 40 mph...

A scantool could tell you what the ECM is requiring for idle, and what it actually is reading from the various sensors... There are a couple of things that can cause a high idle...

Are you totally all of the mounts were replace? Did you or someone you know replace them?

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Old 10-12-2006, 11:28 AM   #3
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I took it to the shop to get the mounts replaced, I was planning on doing it myself but it took a little over one hour to get one nut unloosen and then it was hitting the compressor so I coun't even get it off all the way, gave up and threw it in the shop and they replaced them all for a little over $400. From the looks of it.. all the motor mounts are brand new and it was all installed fine.
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Old 10-12-2006, 11:49 AM   #4
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Your first best bet really is to get the car scanned with a full readout, then make sure you get a copy and tell us what it says or scan the sheet and post that. It will certainly help us to help you if we know what the ECM is seeing.

As far as your hate for Pontiac right now, I understand that you are frustrated right now. We all get that way at some point if there is a particularly annoying/difficult analysis or problem that is giving us headaches. It'* even more annoying when there is more than one thing wrong at one time. But do remember that your car is 17 years old.

Any car that old will develop issues that are larger than the standard maintenance items you would see on a younger car. Things wear out and need to be replaced eventually.

You have certainly come to the right place to seek diagnostic help. The folks here are pretty experienced with this car and likely can help you resolve your issues if you work with them and give them enough information to go on.

EDIT: Oh yeah. And it'* important to realize that when the shop replaced the motor mounts, if the car was reving too high at the time (as it sounds like it was), all they did was fix a result of your real problem. They did not fix the root cause of your problem.
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Old 10-12-2006, 11:56 AM   #5
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I understand, and thanks for any help. Sounds like an ECM scan is the best idea than to jump off spending money and just guessing at it. I'll see what I can do about getting a test ran on it.
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Old 10-12-2006, 02:01 PM   #6
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A malajusted Throttle Position Sensor (reading over .42v at idle) can cause an abnormally high idle (should be 625-725 rpm when warmed up and not over 1500 rpm cold) a high idle will cause a jump when shifting into gear.

Adjusting just is a matter of loosening two screws on the throttle body and rotating the TPS.

Also a coolant temperature sensor reading abnormally low can cause this but generally will not run well.
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Old 10-12-2006, 02:19 PM   #7
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thanks, I'll take another look at it. Last night it looks as if the TPS was rotated as far as it could go and was already hitting, but I'll have to take another look at it.
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Old 10-12-2006, 03:12 PM   #8
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Just to clear things up a bit..
(random img.)


I'm pretty sure the TPS has been replaced before but im not sure when, but when the throttle lever is pulled back (being pushed in pic) the engine quiets down and is not idled as high. So it seems the only adjustment that needs to be done is to the throttle lever or the throttle cable.
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Old 10-12-2006, 03:24 PM   #9
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You can try to make that adjustment... But keep in mind that the ECM can and will adjust to what it thinks the proper idle should be... Even if you try to turn the idle up( just an example BTW ) The cars ECM will still compensate and try to idle ats what it sees as the correct idle for the conditions met..

This is why you want to know what the ECM is seeing, and what its trying to do to correct for the problem... Simply adjusting it may end up being a never ending battle if you don't know what the real issue is...

1) Has the Throttle Body and IAC passages ever been cleaned?

2) I know that the TPS is in a Bad place, but are there any markings that show it to be a unit other Than AC Delco, Possibly wells, GP Sorenson....

You can adjust it if you want to, but make sure the adjusting screw is marked, and you know where the fractor setting is( thats if it hasn't been adjusted in the past by another)

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Old 10-12-2006, 03:36 PM   #10
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yea i just about to state that the IAC/EGR has been changed and I was told it didn't need to be cleaned on the flange and that another gasket wasn't needed. I'm starting to think that might be where my problem is.

It'* and older IAC that came off a Buick and the flange wasn't cleaned and theres no gasket.
Could that be what'* causing the engine to kick around and a high idle?
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