Toypar

Seems to me that these C4 motors are all having idle issues but every one's solution is different. One cause of the problem is that GM used aluminum and steel in combination on these motors. They both expand differently when heated aluminum expands further than steel and it dissipate heat faster. Ranging between many different brands of cars during the many years of use the gasket between the aluminum and steel fail due to the different expansion rates of the alloys and need to be replaced. One new solution that has showed up in the import tuner scene is a heat insulating composite intake gasket that offers better performance and cooler intake air temperatures a technology already employed in the C5 and C6 Corvette

One solution that I can offer is fairly inexpensive, effective and has proven successful for me in the past on many different cars. They usual suspect is when they die on idle, have cold starting issues and surging idle speeds when the check engine light doesn’t not stay lit during KOEO (Key On Engine On) parameters.

Go to your local parts store and buy a Fel-Pro Intake manifold gasket kit, costing on average a MAX of $40.00. Wal-Mart supplies a very inexpensive brake and parts cleaner, engine degreaser and 150-grit sand paper $20.00. If you want to make the intake look new there are many aluminum cleaning agents that will make you intake look NEW NEW .

When you get opportunity pull the entire Intake manifold off the car draining the cooling system first. Clean all gasket mating surfaces with the sand paper then use the parts and brake cleaner on the throttle body and degreaser on the intake. Blow out all bolt holes on the block with compressed air and clean the bolts with a wire brush.

This step is purely aesthetic and is not required but if you’re taking the intake apart now is the best opportunity to make your work look good. Using the engine degreaser or Oxy solution on the intake clean it inside and out using the directions on the bottle, usually soak it in solution and use plastic or nylon bristled brush, an old tooth brush works wonder in those tight spots then rinse with water.

Reassemble the intake using parts cleaner on the gasket surfaces, the key to a successful seal is making sure the gasket sealing surfaces are dry and clean during the whole assembly, use engine oil or never seize on the bolts so you can get a consistent torque on them and look up the torque sequence. Be careful when starting the bolts in the aluminum because they tend to cross thread easily and don’t over tighten the bolts as the soft aluminum strips easily.

Double check your electrical connections and fill the cooling system.

This Method has proven successful for me in the past and I hope it brings you guy’s success.

Good Luck and have fun,

Toypar

Toypar

Dont be scared to throw some input out there guys.

JrRifleCoach

Nice write up.

So, in a nut shell, your fix is to replace the intake manifold gasket.

CFI-EFI

I finally got over my fear.

The only problem is that leaky intake manifold gaskets aren't the most common cause of, and therefore isn't "Everybody's Hard start and Poor Idle Solution". The description of the procedure doesn't reveal any earth shaking, revelations to the process.

RACE ON!!!

zr1fred

Probably one of the biggest causes of hard starting on our old multiport injected cars are the injectors IMO... However, interesting article. As gasoline engines keep getting more and more refined, some of the previously marginal problems get more and more important.

redrose

i have ''fixed'' a bunch of hard start/ rough idle+cruise/ anti-freeze leaks/ oil leaks by simply TIGHTENING the intake bolts...always worth a try before lifting the manifold/ new gaskets (which IS best)...lt1's are esp bad with loose bolts, the back two on the drivers side are routinely discovered to be only finger tight (you'll think your wrench isn't even on the bolt it turns so ez), l98's pass rear two bolts but not as bad.

check yours and report back

Toypar

I have decided to wait on practicing what i preach. I found a 383 stroker shortblock for $1300 internally balanced ect through City Motors. In combo with GM Performace Vortec heads 2.02 64cc and a Edelbrock Vortec TPI Manafold base. Hopefully i can get the ole girl over 400 hp.

Toypar

Taking the intake manafold apart gives you the opportunity to make the engine more appealing to the eye plus just TIGHTENING the bolts doesnt solve the problem it just mask it for a little while. If the bolts on the manafold where loose it is possible that the gasket has coolant, oil vapors and soot between it and the proper seal is not acheived. I have been down the tigtening road and if you really want to run those gremlens out of your motor for SURE rebuild the intake.

Midnight 85

Square

On my 86', I had several things contributing to my bad idle (which is mostly fixed now):

- The O2 sensor was "lazy", it wouldn't cause a "check engine light" but it would send a constant "lean" signal which made the computer dump too much fuel into the engine and that gave me a horrible idle. It was found by using a engine scan tool and watching the O2 sensors output.

- I had a failed weld on an aftermarket intake runner. This was found by filling the intake manifold with smoke and looking for leaks.

- The Harmonic balancer had begun to fail and the outer ring had moved. This cause the timing mark to shift and when I thought I was setting the engine to 6 degrees, it was actually at 13 degrees. Eventually, the failure got worse and I heard a squeaking noise and realized it was bad. Replacing the harmonic balancer fixed this.
- I have some photos of the replacement session here:

http://members.***.net/effergyvette/..._balancer.html

- Shortly after I bought the car I replaced the IAC and cleaned the throttle body, after which the idle moved up to 1100RPM in gear and 1300RPM in neutral. Going through the base idle reset procedure fixed this.