Rough Idle

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Mar 16, 2012 | 11:02 PM

Rocky1974

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Junior Member

Joined: Feb 2012

Posts: 4

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From: Garrison,KY

Car: 87 IROC

Engine: 350 TPI

Transmission: 700R4

Axle/Gears: 7.75in. 3.27 Positraction

Rough Idle

I've been fighting a rough idle problem on my 87 350 IROC for some time and I finally solved it, so I thought I'd post what I found. I have a clean one-owner car with 64k miles. It's been idling rough for quite some time and felt like it had an intermittent miss at just off idle. It also stalled at red lights and it was hard starting. I began by doing a general tune-up, plugs, distributor cap, rotor, fuel filter, and oxygen sensor. I cleaned the MAF sensor. I checked for vacuum leaks and replaced the TPI runner gaskets. I set the minimum idle speed to factory specs. I checked TPS voltage, compression, ignition timing, and fuel pressure. Fuel pressure was low, so I replaced the fuel pump. This solved my hard starting, but not my rough idle. When I set my ignition timing to 6 degrees BTDC, I got starter kickback, so I set my timing to 0 degrees. I also logged a couple of 43's while doing test drives. I also metered out my fuel injectors. They were all between 16.8 and 17 ohms. Yesterday I decided to check timing again and when I started the car with the ESC bypass disconnected, it idled perfectly! I set the timing to 6 degrees BTDC and did a test drive. The problem was much worse. Today I was thinking about all this and decided that I needed to check my harmonic balancer and sure enough, I can see that the inertia ring has moved rearward on its hub. Im sure it has rotated as well. Once I saw this I simply retarded my timing until the idle smoothed out. The car now runs perfectly! I still need to replace my harmonic balancer and re-set my timing, but the car is finally idling correctly.

Last edited by Rocky1974; Mar 17, 2012 at 01:38 PM.

Mar 17, 2012 | 09:59 PM