waynesTPI

My 89 TPI has had a miss at idle since I got it 4 years ago. Recently it has gotten worse and it's time to fix it before the summer. My local machine shop told me the L98 alloy heads have a problem with the valve guides getting loose and floating, causeing the rough idle. Yet at cruise there is no noticeable problem. I have no clue as to how many miles are on this engine. Does this sound like a possible explaination to the miss?

bogus

damn. your machine shop knows nothing of what they speak...

the valve SEALS go bad, causing oil leaking. As for the guides? if they moved, you would have some much bigger problems, and it would be all over the rev range, and, it won't last long before one of them jammed. Which would be bad.

More then likely, you have a miss caused by a bad wire or plug.

I would start with a simple tune up and move from there.

If it isn't a tune up related problem, it is valve related, but I would bet it's a lazy lifter or a bad rocker or a rocker out of adjustment.

Z51L9889

As bogus suggested, check the plug wires and vacuum hoses. Also, check the idle air passages in the throttle body to make sure they are clear. They tend to get a bunch of carbon build-up over time. Remove the hose from the throttle body, open the throttle plate, and rub the inside of the throttle body with carb cleaner until the carbon build-up is gone.

waynesTPI

thats why I asked here. It has had a full tune up so the other possibles you mentioned make sense. I hadn't planned on giving the shop my heads for a rebuild as I can't do with much down time. my plan was to buy a new set of stock alloys and do the job over a weekend. maybe I should have a set of lifters on hand also?
I have to stand emissions testing here on the ant hill so the engine is bone stock, but this old disabled vet likes his performance too. So I'll listen to all suggestions on heads or lifters or any thing else I should do while its down.

cv67

I doubt its your heads...An EGR valve and injectors usually solve the rough idle in vettes, considering all tune up parts are new. Of course, wer'e all guessing. I'd check for codes, decarbon your entire intake tract, clean the TB, free stuff that you can do first. Take it from there.

waynesTPI

my wallet and have the Diacom software for reading all running values and pulling codes. The EGR was changed while the tubes and phleum were off for another reason and that made no difference. I usually use a bottle of Techron twice a year but have never changed any injectors to date. Besides the rough idle and not passing the emission tests it runs good enough to **** off my son with his 9C-1 96 LT1 caprice

Mad-Mic

while you have the throttle body off pull the IAC and clean that real good same way. carb cleaner. that should smooth out your idle.

waynesTPI

I will print out this thread. another reason I'm doing the big weekend job is a coolant leak on the manifold to head thats has been there for a couple of years. I have heard that I should use the Fel-pros instead of the OEM ones, is that correct?

cv67

Fel Pro's Might as well put injectors in if yours are original and have it torn apart.

jfb

At night in the dark with the engine idling, look at all of the plug wires and see if there is a spark to ground along their length and at the spark plug boot. Are all your plug wire guides intact? The guides keep the plug wires away from grounded metal which can cause the spark to jump through pinholes in even new plug wires. New or not, measure the resistance of each plug wire, they should be approximately 5000 ohms per foot and wiggle each end to ensure that the ends do not have intermittent connection ( ohmeter should remain steady when wiggling).

olman

I had an injector make mine act like that an it didn't have that many miles on it. Ignition can do that too.

Alzado77

Just a thought but make sure nobody has installed a modified chip. I had one installed and it would cause a slight miss as you described. Took it out and installed an original and it went away. I've since had one burned that turns the fans on earlier but didn't have anything else modified. For some reason my corvette only likes the original chip.