Dear All
(I am Moe_Vette but password seems to fail)

I am in England and posted a few weeks back about me 92 Vette have the head gasket job done. Well its 3 weeks later and the shop has finally got her rebuilt BUT they are having an issue with the idle post the engine rebuild. I asked them for a description of the issue so I could post it with you good folks - I am writing it exactly as it came to me via a text - they wrote


The issue is that the idle is a little erratic and running higher than it should at approx 1200-1300 rpm. Under engine load (higher revs)by the driver foot at stand still or driving the car seems fine. Also we no longer have any error codes either which is good - a step forward.

Now these guys are an engine performance shop so I imagine what is up is not the norm or obvious. They did mention they removed the egr valve when they put the engine back together (as it broke) I understand this should impact anything as it cycle exhaust gases back though the engine for the sake of emissions - is this the case - could this account for the idle? They also swapped out the thermostat too.

Any thoughts would be greatly appreciated - seems only the high idle is keeping her from me - any ideas appreciated because I am in full withdrawals - been 3 weeks - going mad !

many many thanks

Sounds like a vacuum leak.

No codes means that the IAC is connected.

I will also fix up your password...

Thanks Bogus you kindly wrote

Sounds like a vacuum leak. No codes means that the IAC is connected.

Pretty sure they have looked for vacuum leaks (are they tricky to spot?), Yes there are no code showing anymore - forgive me the IAC is connected ? this is good right?

Many thanks

You wont get a code for an IAC. When dealing with my 93 for 15 plus years, I had idle issues and finally an older gentlemen showed me the drawing that shows you how to test your IAC. The ECM will only who you what the ECM is telling the IAC it needs it to do, not what it is actually doing. Never understood that.
http://shbox.com/1/iac2.jpg
On the 92 there are a few vacuum areas to look at on the manifold, other than that, there isnt much to cause this. i would say the IAC is bad. And if it has been taken out and twisted or pushed in, it will break easily.

Quote:

I'd be suspicious of this, as elininating the EGR valve has the potential for creating an ENORMOUS vacuum leak if it wasn't done properly.

If they removed the EGR valve, did they install a block-off plate on the intake manifold where the EGR valve used to be? And if they did install a block-off plate, are they sure it's COMPLETELY sealed? They can try to spray a little carburetor cleaner on the manifold around the area where the EGR valve was while the engine is running to be sure (if RPMs jump up when the carb cleaner is sprayed, there's your vacuum leak). I'm also assuming that if they removed the EGR valve, they also removed and plugged the EGR tubing to/from the exhaust manifolds/intake manifold. The tubing from the exhaust manifolds connects to the back of the intake manifold on the passneger side. If that tubing was removed, they'll want to make sure the port on the intake manifold is properly sealed too. Finally, they'll also want to make sure that they've blocked the small vacuum line that comes from the intake manifold to the EGR solenoid (driver's side of intake manifold, underneath the fuel rail cover).

By the way, if they broke the EGR valve while repairing the head gaskets, why didn't they install a new one for you?

This is what happens when I try to answer when talking on the phone! Stupid me.

Yes, the egr would cause a problem if the blocking plate wasn't done right. Same goes if the riser tube from the exhaust wasn't sealed properly.

I am a fan of taking some carb cleaner around the intake and see what happens there.

@Steve - you are right! I forgot that the early ECM didn't check the IAC, just told it what to do... and hope it did it!

NO JOY

Thanks for all your fine suggestions - seems they covered these bases. On top of this now the car is fire only on 7 cylinders - they said they have seen it get worse over the past few days - they are coming by my house tonight to pick up an old opti-spark (long story but had it swapped out coz she would not start on wet days - was not the opti - turned out to be plugs and cables !) So I have a perfectly good opti in my garage for rainy days (pun intended

They are sure the egr valve was closed up (did the spay tests etc) they printed of your stuff this morning to go over it - thanks again.

Seems to me if the idle is getting worse (was running on 8 cyls after head gasket work - but has slowly degraded to 7 since over past few days) that a plug has slowly worn/deteriorated - does that sound feasible - one of the spark plug holes did have water in it as a result of the head gasket issue - could there be residual water mucking up the plug?

I went to look things over today - apparently the egr was wrecked when they stripped the engine down to do the gasket work - very sad to see - but I did also install 2 new 285'd on the back - god I miss her !

Thanks for all your help - any other thoughts greatly appreciated as she is still on the ramp

Tell them to fire it up at night (dark, no lights on) and look for any arcing from plug wires, pay attention to the coil to opti wire as well.

I wonder if the heads are torqued right... the plugs cylinder should be dry.

I would double check head torque at this point. Check and clean plugs (unless the gap has grown - .050" - it won't fail).