96 LT1 CE: I am having a problem with a skip when idling, not all the time just when it is warm and the idle is around 750-800 rpm. I've had the OBD II checked a few times and no codes are coming up. The mechanic diagnosed it as a cylinder that is missing, but couldn't figure out which one. Based on a post I saw yesterday in the General Forum for C4's here, I am beginning to wonder if it might be the MAF. The other thing I have noticed is that most of the vacuum hoses are original and slowly disintegrating.

Do either the MAF or vacuum hoses seem to be possible causes and how would I diagnose the MAF before I spend money replacing it?

 

blow cigar smoke in the hose going to the brake booster and see where it comes out on the engine. and look at it in the dark for arcks and sparks by the plug wires.

 

I'll need to find some other way of generating the smoke because nobody in my family smokes and the smell of cigars make me sick, but thank you for the suggestion. I'm leaving town tomorrow morning, but I'll be back just before Christmas so I'll come back with the results then. Where should I see the smoke come out?

 

I have a '96 also and when I first bought it in 2012, I carefully went through an inspection of the car. I replaced every vacuum line in the engine bay after finding that they were either dried out and cracking or "wet/slimy" and falling apart. I also started checking and cleaning every ground connection I could find (after disconnecting the battery).

Also check the venting system for the optispark distributor - pull the plastic cover for the fuel injectors on the drivers side and you'll see a vacuum hose coming off the intake manifold with two small white/blue discs inline in the vacuum line. Pull the line off the larger disc that is second in line to the manifold and look at the side going to the manifold. You'll see a small metal orifice that often gets plugged up causing a restriction in the venting system.

If you don't already have it, get a factory service manual (two volume red cover edition Bishko CD version) on Ebay. Also get a Mityvac vacuum/pressure tester to test the opti venting system. The manual will have diagnostic trees to diagnose starting and running problems along with DTC (diagnostic trouble codes). Also get a OBDII reader as the '96 is OBDII compliant and DTC's can be read and erased with the reader.

As a last check while you're waiting for the manual, pull the car into a dark spot at night and open the hood while running. Look for any arcing or sparking around the opti, coil and spark plug wires especially near the spark plugs. And don't forget that your O2 sensors (two front are involved in fuel delivery) are probably 20 years old and may be causing problems intermittently.

Good luck.

 

The usual way to diagnose a bad cylinder is to unplug the injector connectors one by one. The one that doesn't cause a change in RPM is the bad one.

 

If you know someone with access to a Tech2 scanner it has a misfire counter in special functions that may indicate what cylinder. I suggest to fix the obvious - vacuum hoses - with no clue on miles a maintenance type tune up may help. If MAF isn't setting code visual inspection is about all the diagnosing you do. You can wiggle connector, make sure intake boot is on correctly not folded over and clamp is tight. You can look in the "Barrel" for build up on wire or film - several companies make cleaners to service MAF and throttle body. If you use a "K&N" style air filter and over oil it the excess oil can cause MAF trouble or failure. If the engine runs better with MAF unplugged; that can indicate a failing MAF. If car is not used often or just putts around town...it could be carbon build up and it just may need driven in second gear or until black clouds stop appearing when you "punch it"

 

Thanks for the all the tips. It has 119K on it (116K when I bought it in March) and I replaced the plugs and wires almost right away. I don't recall whether or not it had the skip prior to that because I replaced them so quickly after buying the car. Unfortunately I don't know anybody with a Tech2 scanner so for now that is a dead end. I'll start with the vacuum hoses and looking for sparks in the dark. I think I've double-checked the intake boot, but it won't hurt to do it again. I am using a K&N so that might be a clue. I'll be home lat tomorrow, but I won't be able to get started on this until Christmas day.

 

when you replaced the plug wires did you put a bit of dielectric grease on them and made sure they all clicked twice?

 

Are the front two O2 sensors original? If so, since you have passed the 100k point, I would think about replacing them since they are also now 20 years old.

Here's a good read on O2 sensors -
http://www.autotap.com/techlibrary/r...aintenance.asp
and another -
http://s7d9.scene7.com/is/content/GenuinePartsCompany/1704119pdf?$PDF$

 

if you have a miss there would be a CEL with code stored. I get codes without any noticeable change.

 

Put timing light on one wire at a time. Will tell you if it electronic