Still trying to trace down my idle issues (normal RPMs and rough when cold, smoother but high idle when warm, lean BLMs). I just recently went through the EGR testing procedure in the FSM, and thought that my results were normal, but now I'm not sure.

Part of the test procedure was to attach a hand vacuum pump to the manifold side of the EGR solenoid, and a vacuum gauge to the EGR valve side. Then, "energize" the solenoid by jumpering pins A and B on the ALDL, and turn the key on, engine off. At this point, the manual calls to apply 10" of vacuum at the hand vacuum pump and ensure that the same number registers on the gauge. When I squeezed the vacuum pump, the needles on the pump gauge and the vacuum gauge moved, but barely (maybe 1" or 2" of vacuum) and whatever vacuum I applied quickly bled off. I had to squeeze the handle several times fairly quickly in order for the needles to reach the 10" mark, and still, all of the vacuum immediately bled off.

When this happened, I thought that this is normal operation from the solenoid, since when "energized" it is allowing vacuum from the manifold to pass through to the EGR valve. And since there's supposedly nothing in the solenoid to "hold" the vacuum, it would just immediately bleed away. However, if you read the final two posts on the last page of this thread: http://www.corvetteactioncenter.com/...onsistent.html
the car's owner stated that after replacing his EGR solenoid, his problem cleared up. He also stated that the NEW solenoid, WHEN ENERGIZED, still held vacuum on the vacuum gauge.

Since my issue is most definitely false air coming from SOMEWHERE, and all attempts at finding the culprit through normal vacuum leak troubleshooting have produced no results, is it possible that I could have an "internal" vacuum leak at my EGR solenoid?

Thanks in advance!

Ron

 

Since my issue is most definitely false air coming from SOMEWHERE, and all attempts at finding the culprit through normal vacuum leak troubleshooting have produced no results, is it possible that I could have an "internal" vacuum leak at my EGR solenoid?

Have you physically removed the EGR valve diaphragm and inspected it for cracks? Mine was dry-rotted from years of under hood engine heat and it was glaringly obvious it was leaking. I'll bet that's your case, too.

The EGR valve's held in place on the rear of the intake plenum by two 8 mm bolts.

 

Sounds like a bad EGR to me.

 

I haven't actually removed the EGR valve from the manifold, but I did put 10" of vacuum directly on it and it did hold, and I also moved the diaphragm while the car was running and it does start to bog the engine down. The diaphragm does seem fairly stiff; it doesn't feel like 5" or 7" of vacuum would be able to move it, but it does at least seem to respond fairly well.

Man, I really hate replacing parts unless I know beyond a shadow of a doubt doing will fix a problem, but I'm beginning to wonder if just putting a new EGR solenoid and valve on might be my next best move.

 

So, only because I hate technical troubleshooting posts that are left open with no final resolution, I'm glad to say that I replaced my EGR solenoid and EGR valve and about 90% of my surging idle issues are gone! It still surges a small amount from time to time, but she's MUCH more driveable. I found that the seal beneath my MAP sensor is quite a bit deformed too. I have a new one on order and I'm hoping that's the final key.

Ron

 

Ron,
Im glad you did post your final resolution, more people should do this, it helps out the next guy that has the same problem.....WW

 

Not trying to rebuke you, but had you physically removed the EGR assembly as I suggested, you would have known without a shadow of a doubt if you had an actual EGR valve diaphragm issue.

It's really not that hard to get at on an LT1. Glad you got significant resolution to your issue, though.

 

You can check to see if the diaphram is cracked or broken by just shooting some throttle body cleaner under it while the motors running. If the rpms pick up then the egr is bad.....WW

 

You should have inspected the EGR passageway for carbon buildup/blockage when you removed the old assembly, too. I'm not saying you didn't, just that it's a good idea to check.

Many people have bolted on a new unit without checking the passageway, too, resulting in poor/diminished EGR system performance and Code 32 that continues to be stored on their ECM.