1985 Oldsmobile 98 Rough idle even in drive range-no back

CFOXZ

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1985 OLDSMOBILE 98
6 CYL
FWD
AUTOMATIC
80 MILES

Replaced motor, Has about 80 miles on it. All components except throttle body fuel pump and fuel rail harness. No codes on check engine except normal 1-2. Once accelerated it runs good, lots of power. My shop mechanic can't figure out the problem and he is a very good mechanic. I have all the shop manuals for it. Could a dirty sock on the fuel pump or pulsator be causing the problem? Also replaced some of the firewall relays. Also where can I get a Dorman replacement fuel injection wire harness? Your list does not go down to 1985 Thanks, Chaz

5 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

Hi
So I understand the problem idle is rough as in miss or low? Does it smooth out with bringing RPMs up?
Unplug MAF see if idle smooths out. Has TPS and ISC been ruled good?
Let me know
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Friday, November 20th, 2009 AT 3:11 PM

CFOXZ

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6 POSTS

Map sensor is new. Iac motor is new. Tps is working ok. New Distributor, and cap. Car does run smooth except when it is not moving- in drive, reverse or park. Has full power on acceleration. No check engine light. Codes check out with 1-2 all ok! New fuel filter, new fuel injectors, new spark plugs- not Bosh platinium. Egr ststem has completely replaced. And new plug wires. Starts up with a fast idle and comes down to normal in a few seconds and then idles rough. Weird! Thanks, Chaz

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Friday, November 20th, 2009 AT 8:57 PM

CFOXZ

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6 POSTS

My mechanic solved the problem! The New Distributor Cap from Autp Zone was defective and firing on 4 strong cylinders and 2 very weak ones and the connector tips were all sloppy loose. Second time got bad part from them. Will not use any Bosch iparts either. But have a question: My 2 front motor mounts need replacing. Can you tell me which mounts I will need to replace and are there Hydraulic mounts on the tran mounts. Should I get all the mounts replaced- motor and trans? My shop manual is not too clear on them. Thanks Chaz

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Saturday, November 21st, 2009 AT 4:49 PM

DOCFIXIT

MECHANIC
18,828 POSTS

Great news yes Auto Zone not best on parts use NAPA myself. As for mounts early design solid rubber later design hydraulic. Can use either hydo or gas smooth out vibs better. As for trans if 440-T4 hydraulic 4T60-4T60TE solid mount.
New engine new mounts would be the way to go.

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Monday, November 23rd, 2009 AT 9:34 AM

CFOXZ