Changed rotor, cap, plug wires and plugs and timed to 7 degrees. I found the plug wires at 120,000 had never been changed and had some problems, the rotor was bad and so was the cap..Thought I had the problemd for sure.but I still had a irratic soft ruff idle when it gets really warmed up...the vette idles at 7 to 800 RPM...When it heats up it can falter at an idle and go as low as 600 and the back 700 or 800rmp. The plugs I pulled look great, good color etc...us the standar AC plugs recommended.

I am worried it is a valve, but the miss or not consistant. YOu can jump on the vette and its 6sp and it is like grease lighting..and smooth. I am wondering if it is a valve, maybe a vacuum leak...I have no codes of any kind.

After it heats up and is idleing at 700 i get a slight back lash on the crank and clutch and you can feel the ruff ness in the 6 spds shifter if your quite. It is almost metallic but it is to soft. I have run heavy cams in my V Drive boats and got drive line back lash which is normal but that is really noise, but this is like that but so much quiter.

I am at a loss...Maybe I should do a compression test...Maybe an injector is bad...If it heats up and is worse maybe vacuum...being not consistent but irregular I hope it is not a valve. I have flowmasters so it is easier to here this ruff odd miss or what ever it is.

Any buddy have any ideas or have experienced this and if so what did you do.

Thanks for any feed back of any kind.

Bob in stockton :grouphug: :confused:

 

To rule out any ignition problem clip a timing light in turn onto each wire and see if the engine miss coincides with missed flashes on any wires.

If no problem there you might clean the IAC pintel & it's bore as the ECM uses it to maintain idle.

Since it happens when warm we can assume the ECM is in closed loop mode. You can use the ECM's diagnostic mode detailed on my site (link in sig. below) to assure that the ECM is going/staying in closed loop.

Since your plugs look good and the same at each cylinder I don't suspect an injector but you can place a finger in turn on the connector of each to see if the engine miss coincides with a missed injector pulse.

After these with no success I guess a compression check might be in order.

 

Thank you I appreciate the help...I will try all those things and end with the compression.

Again thanks again

Bob :hurray:

 

Any of those things can cause a miss. To check to see if an injector is stuck open, hook up a fuel pressure gauge at the rail and shut the car off, the pressure should hold for several minutes. If it doesnt, one or more is likely bad. If so, replace all 8 or have all of them cleaned/serviced at CruzinPerformance.

Vacuum leaks and ignition problems are usually the causes though.

 

The year of your car indicates a potential problem with your injectors. The 89 model has GM Multec injectors which are prone to short out. Take an ohm meter, unplug each injector and measure the resistance across the two connections on the top of the injector. You should have about 16 ohms. If you find ones in the 10 to 12 ohm range (like I did on my 89), you may have injector problems. An easy check will verify you do or do not have this problem. If you need advice on injectors, I have a good source! Hope this is helpful.

 

I would be curious to see what the ECM is seeing. I had a great software program called EASE, put it on a laptop and see in real time what every sensor is detecting. A 4 gas analyzer's probe can be put into a tailpipe and can help reveal combustion conditions.
I would consider a leak down test also. Of course visually looking at actual engine components is good too. Like underneath the valve covers. Getting readings from the fuel rail via a fuel pressure gauge too. A volt ohm meter can do wonders. Can ya tell I like toys?


[Modified by 89 Paul in Cal, 6:57 PM 12/17/2003]

 

As they say guys this input is really where the rubber does meet the road. I am pretty technical and this input you all are giving is like a breath of fresh air. I will perform all the tests...The injector, ohm meter test, at 16 ohms, is a real inside scoop...The ECM in loop or not loop is great to. I will pop the value covers but before I do that little job in itself I will do injectors, compression, and leak down on the fuel rail. Gosh everyone thanks again.

Bob :seeya :party: