Hello,

I’ve checked a lot of posts and have been working my way through the check list of trying to solve my rough idle problem. I think I’m leaning toward the M/C solenoidbeing the culprit but I wanted to check with all the gurus out there if there’s something else I should check first before I drop 80 bucks on a new M/C solenoid. I’ve posted all the details below and all the things I’ve tried so far. I very much appreciate any and all advice!

Steve

The car:

- 1984 Trans Am, stock from what I can tell,5-speed, 4 BBL Q-jet, VIN H
- Bought a couple months ago
- Has always had a rough idle since I’ve driven it
- 99K miles on the car
- Don’t know anything about the history of the car other than it was made at Van Nuys and there’s no rust on it, so I suspect it was a west coast car, pretty well taken care of but has probably been sittingin its most recent years. I drove it from Michigan (where I bought it) to Virginia without troubles other than therough idle.

Problem description:
- Missing at idle speed / rough idle
- Starts up good, no problems with the fast idle setting
- Regular Idle speed fluctuates between about 600-750 rpm
- No surging, idle stays pretty consistent within that range
- Sometimes will stall while idling, but not too often
- No hesitation when accelerating, runs good at speed
- Check engine light will illuminate at long stoplights but goes away once accelerating
- Trouble codes alternate between 13 and 44 after weekend drives (O2 circuit, lean mixture)

What I’ve done so far:
- Replaced spark plugs and wires
- Adjusted ignition timing
- Replaced O2 sensor
- Checked throttle position solenoid (TPS)(receiving 4.95V, smooth increase in resistance as throttle opens 0.224 to 0.4(2M Ohm), no drop-outs in the reading
- Checked and adjusted idle air control (IAC) solenoid
- Checked ground wires
- Checked for vacuum leaks, replaced a few suspect hoses, but most wires and hoses are generally in good condition
- EGR diaphragm still moves without too much effort – seems ok
- Replaced charcoal canister filter
- The electric choke was not working when I boughtit so I replaced that. Choke works fine now.
- Probably not related but I replaced the thermostat because my temp keeps reading low – only about 150-160 degrees when warmed up. But that didn’t help though,so I’ll have to figure out what else is going on there.

 

Make sure the egr isn't getting vacuum at idle.

 

Thanks - the EGR was the culprit! The valve itself is fine but the port was clogged with deposits and the gasket was toast. Cleaned it all out, new gasket, and it idles great now. Glad I did that before tearing open the carb!

thanks,
Steve

 

That's good work!