Car running Rich at idle..need help!!
 

I have checked everything I could find in the GM service manual - I adjusted the air/idle bleed valve on the carb using a dwell meter (6 cylinder scale) at 30 degrees, I also ensured the Mixture control solinoid was operating correctly, checked the resistance at the ECM terminals, replaced the ECM (had a spare). I have no codes whatsoever from the ECM. The only thing I have found that could be wrong is the Air Management Control valve. From what I've read in the manual, when the engine is cold and in open loop, all air from the air pump is supposed to flow to the exhaust manifolds (Ported mode), and when the ECM goes closed loop, or three minutes whichever is first, the Air Management Valve shifts all air output from the exhaust manifolds to the Catalytic Converter. Well, it seems that the valve stays in Ported mode and pumps air into the exhaust manfold constantly (doesn't shift), which from what I read, can cause the ECM to think the car is running lean, so it sends a fuel rich signal to compensate. Does this sound correct?? Or am I overlooking something? A new Air Management Valve will cost me $100.00 at the parts store, so I would like to get one from the junkyrd if possible, but how can I test if it's good before I buy it?? Any help would be greatly appreciated.

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Freshly rebuilt 19831/2 or 3/4 Camaro Z28 305 H.O. 3:73 Gears, BW T-5, Duel Snorkle, Rhino Clutch, 2040 Compu-cam, LS1 valve springs, porting, PST front end kit, K&N Filter and runs great but ain't streetable yet!!....Future Mods: Not yet decided if I'll keep it!

[This message has been edited by Confuzed1 (edited September 12, 2000).]

Anyone?????? Surely someone has had this go bad on them before... can it really cause it to run rich at idle, and how can I check one on a junk car to see if it's good before I buy it?

The easy way to test your theory would be to just drive it with the smog pump belt removed. Thus, no extra air will be being introduced into the exhaust, causing a false lean reading. Your diagnosis sounds correct, if the AIR system is operating in ported mode during closed loop operation, you should experience a rich condition as the ecm incorrectly tries to compensate.

How do you know it is running rich at idle? If the air pump was really the culprit, it should run rich under all closed loop operating conditions.

Finally, have you checked the TPS voltage?? If it is indicating a WOT voltage at idle, the ecm could go into WOT open loop mode, which is pretty much full rich with the MC solenoid.

Good Luck!

My only concern is that I am not positive the ecm controls the mixture at idle. I suspect the idle mixture is the exclusive domain of the mixture screws, and the M/C solenoid and O2 sensor only come into play when the TPS indicates greater than idle position. Don't quote me on that, however.

CF1/Drew,

The ECM does control the mixture at idle, at least on a Rochester E4ME. If your diverter valve (Air Management Unit) is stuck, unstick it or bypass it so that all the air is pumped to the cat all the time. The extra air at cold idle is only intended to heat the O2 sensor more quickly and offset the negative environmental effects of the intentionally rich cold-starting mixture. For the purposes of diagnosis, it would be perfectly acceptable (and legal) to alter the valve operation in such a way. The O2 may take a bit longer to report good data, but should at least not be indicating a false lean condition. By the way, how old is the oxygen sensor, anyway?

I think you've already found the source of the problem. The next step is to repair it then probably reset the idle mixture solenoid and TPS voltage. If you're lucky, the mixture solenoid duty cycle will still be close to 50% (30°).

If you still experience a rich condition, you may need to inspect the inlet needlt and seat and set the float level.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

Thanks for the advice all!
UPDATE: I checked votage from TPS at idle and W.O.T - Checked OK
Bypassed my Air Management Valve by connecting air pump outlet hose from pump outlet to the manifold. - Still runs RICH at idle (Burns eyes etc...)
Adjusted Air Bleed Valve using dwell meter in closed loop - set at 30 degress - Same Problem.
VADER : I didn't look at the float needle and seat or adjust the M/C solonoid because it would void the warranty. It's a fresh rebuild, (the second) I've had 2 rebuilt carbs and have had the identical problem while runnuing with both of them, so I'm not leaning toward the carb as the source of the problem.

So, I still have the same problem with idling rich, along with a slight "surge" of around 100 RPM (from 700 to 800 RPM). I even removed my EGR Valve and installed a "block-off gasket" to see if it was actually leaking - SAME THING!! I'm at a total loss at what is causing this. Can anyone think of another thing I should check to fix this once and for all??? (please be nice!!)

I think I'll replace my intake gasket, although I could'nt find a leak after spraying carb cleaner around the edge of the intake at idle. Might be a small leak maybe. ANYONE?



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Freshly rebuilt 19831/2 or 3/4 Camaro Z28 305 H.O. 3:73 Gears, BW T-5, Duel Snorkle, Rhino Clutch, 2040 Compu-cam, LS1 valve springs, porting, PST front end kit, K&N Filter and runs great but ain't streetable yet!!....Future Mods: Not yet decided if I'll keep it!

CF1,

How is the PCV valve?

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

VADER,

I had installed a new PVC Valve during the rebuild, I also checked it with the engine running. Pulls a vacuum with the engine running, and rattles if I take it out. I also have a new Knock sensor and Vacuum sensor too. I checked the adjustment
the air/idle mixture screws also. I turned them in until lightly seated, and backed them out three turns....still runs rich. After that, I turned them both outward an additional one turn, and the car idled great with no surges at all when cold, but when it warms up, you can tell when it goes into closed-loop because it started to surge again, and running rich. Shouldn't I get a code?? I have no SES light on at all, no codes, and yes, I replaced the friggin ECM too. Boy this car is really pissin me off pretty good. Thanks for all your suggestions so far....got any more??? I'm at a crossroads with this project, and I'm almost ready to rip out this computer, carb and distributer and exchange them for REAL ones.

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Freshly rebuilt 19831/2 or 3/4 Camaro Z28 305 H.O. 3:73 Gears, BW T-5, Duel Snorkle, Rhino Clutch, 2040 Compu-cam, LS1 valve springs, porting, PST front end kit, K&N Filter and runs great but ain't streetable yet!!....Future Mods: Not yet decided if I'll keep it!

CF1,

I'vre always had fairly good success starting at 1-1/2 to 2 turns open for the idle mixture screws. Since you're regulating fuel with the screws instead of air, opening them more would enrich the idle mixture.

If it goes rich most notably when the ECM enters closed loop mode, I would suspect you are getting an incorrect signal from the oxygen sensor. I never did find out how old your current sensor is, and Drew mentioned the sensor, too. They do degrade over time, and are easily contaminated by RTV sealers that are not labelled "Sensor Safe". Once this occurs, the zirconia element in the sensor is useless, and you need to replace it. You might also want to check the electrical connection at the sensor and the exhaust ground integrity. I know it should be well-grounded, but new gaskets and fresh paint on the bolts and headers may be insulating a bit.

BTW - THIS is a CheeseHead... (yup, Verba and the convict autographed it.) http://homestead.juno.com/jlstrey/files/cheesehead.jpg

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

[This message has been edited by Vader (edited September 21, 2000).]

VADER—

I have thought about the O2 sensor, but that sensor was also replaced with a new one during the rebuild 3 months ago. Sounds like a good possibility it could cause the richness in closed loop only, so I suppose it wouldn't hurt to check it any way.
I've checked the TPS, and it checked OK with the Sun meter. I think I'll also try making an initial adjustment of the air/fuel mixture needle valves as you suggested, and set them at 1 1/2 turns from lightly seated vice three turns.

I appreciate all the suggestions so far, and I’ll let you know what happens! I’ve experienced some off-the-wall problems with this car every since I bought it. I knew it needed some major work, and that’s all done. It’s all these little “bugs” that are getting real frustrating. It DOES seem to have plenty of power off-idle though, so I’ll keep trying.

BTW,

LOL at the “cheese head” thing. But Mark Chumura isn’t a convict quite yet, but it doesn’t look good!! He’s in the news everyday around here. It appears his lawyers are trying to find a “catch 22” to get him out of it altogether, but I doubt that will happen. Let this be a lesson that everyone can learn from – get an older, ugly babysitter so this kind of thing doesn’t happen!!!


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Freshly rebuilt 19831/2 or 3/4 Camaro Z28 305 H.O. 3:73 Gears, BW T-5, Duel Snorkle, Rhino Clutch, 2040 Compu-cam, LS1 valve springs, porting, PST front end kit, K&N Filter and runs great but ain't streetable yet!!....Future Mods: Not yet decided if I'll keep it!

Re: Car running Rich at idle..need help!!
 

Sounds like my car got an 84 put a cam cap rotor plugs wires and tps . Still has a slight ****in miss