Weird Engine issue

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Feb 14, 2012 | 12:28 AM

kdtomczak

Thread Starter

Instructor

Joined: Jan 2012

Posts: 192

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From: Columbia SC

Weird Engine issue

In my 86, sometimes when i'm at a stop light or in park, my engine will feel like someone's pressing the pedal in a rhythm. The car will even try to pull forward while I'm holding the brake..

Anyone know what could be causing this?

Feb 14, 2012 | 07:49 AM

AGENT 86

Team Owner

Joined: Jan 2003

Posts: 20,320

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From: Summerland B.C. Canada

You might want to start with looking for a vacuum leak.

Feb 14, 2012 | 09:38 AM

Goldcylon

Tech Contributor

Joined: Aug 2006

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From: Peoria Arizona.. Resident Gold Cylon

Throttle adjustment ?

Feb 15, 2012 | 07:27 AM

Keystring

Drifting

Joined: Aug 2006

Posts: 1,624

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From: Canandaigua New York

Besides the suggestions above, you could also either have a bad Throttle Position Sensor or a dirty MAF sensor. (I think 85 is MAF and not MAP).

Last edited by Keystring; Feb 15, 2012 at 07:58 AM.

Feb 15, 2012 | 01:38 PM

BroCorvette

Instructor

Joined: Sep 2011

Posts: 131

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From: Illinois

Quote:

Originally Posted by Keystring

Besides the suggestions above, you could also either have a bad Throttle Position Sensor or a dirty MAF sensor. (I think 85 is MAF and not MAP).

Correct 85' is MAF only.

Feb 15, 2012 | 01:50 PM

383vett

Race Director

Joined: Apr 2003

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From: moraga ca

Does your car have a roots blower and dual carbs?

Feb 15, 2012 | 06:51 PM

John A. Marker

Le Mans Master

Joined: Mar 2004

Posts: 5,107

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From: Dublin CA

Check TPS and then the AIC. It could be that the AIC passage has carbon build up.

I would think that if you had vacuum leaks the problem would be more constant.

Feb 15, 2012 | 07:24 PM

SunCr

Le Mans Master

Joined: Dec 2000

Posts: 7,839

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From: San Diego, Ca

ECM may be trying to compensate for some load that doesn't exist and that's usually a/c or if an Auto, a neutral/drive signal. With either input, the ECM increases/decreases IAC counts and pulse width to maintain whatever is targeted for idle speed. If you hook up a scanner, you can look at the data stream and find out if there's any signal that shouldn't be there. Note if it is a/c - these early years aren't perfect in matching compressor load to idle speed and you can often feel the load of the compressor as it cycles, though it shouldn't be severe enough that you need to stomp on the brakes to keep it from moving forward. If the condition is intermittent, that may be all that's happening, as compressor cycling depends on ambient air temp and charge. If you can get the data, you should be able to figure it out.