Monster231

I have noticed more and more that my idle has become increasingly rougher. This has been going on over the past year. Fist i thought it was my battery, because i had probelms with it before. I installed a new red top and even changed the connecting bolts on the wires becasue one was cracked. It improved a bit but still there. Next i changed my plugs and wires, i noticed that one of the wires was craked, so i replaced them with msd's and NGK plugs. It got better but still there. I took it to the dealer ship to run the codes and Jason the tech ( he's awesome) said there were no codes what so ever. He told me to try a top engine cleaner. I did that today and noticed a big improvement in performance but, the stubmle and hesitation is there.
The symptoms:
It i put it into a big gear -5th or 6th- at lower speeds it stumble and hesitates all over the place. It fells like a misfire, but the car is very stong at rpms over 2K.
At idle, if i turm my AC on the cars starts to stumble all over the place too. but if i hit the gas, everythings OK. All the problems seem to happen at lower RPMS underload. Any suggestions

pewter99

hmmmm..air leak?? are your connections good between air filters, airbridge and MAF..unmetered air could cause it..you changed plugs and wires already so....

Bill Curlee

Secondary ignition voltage (high voltage from the coils to the plugs) will not usualy set a code that is readable on the DIC)

Try to get the car to stumble. When it is running bad, see if your check engine light is flashing? When it is flashing, check the DTC codes and see if you get a PCM 0300 code. That indicates that the PCM has detected an engine mis-fire. If the mis fire is bad enough and present for lone enough the code will set and remain in memory.

If you see the P0300 code there are a few thing that can cause that code. Cracked plug, wire not on all of the way, damaged wire, bad coil, ect ect.

When your car is under heavy load the coil needs to produce the most voltage to fire the cylinders. Under light loads the voltage to fire the plugs is low. If there is ANYTHING wrong with your secondary ignition system, it will show up under heavy load. Try spraying water on one plug and coil at a time and see if it causes a miss It should NOT hurt anything and may show you where the bad component is.

Here is what happened to one of my plugs during a header install and it caused the same symptoms.



Did you use any silicone dielectric grease on your sparkplug wire boots??

Please let me know how you make out.

Monster231

great post, I will check those tommorow!!

T_Vert

if you have HPT u can monitor cylinder misfire counts. If you want im in elgin I can scan it for u and figure out what is going on or at least pinpoint it to a cylinder/bank.

Dave

VetteTech81

Exactly, this would be my first step, you could have a coil failing possibly. But you need to know where to look.
-=Rick

Monster231

Thats awesome..... I think ill take you up on that, can you PM me or email me a number where i can get in touch with you

T_Vert

removed #

Elk

I finally solved a similar sounding problem. I had the same symptoms for quite a while with no codes. It kept getting worse. Finally it I code a code indicating a problem with the rear knock sensor. I just replaced both knock sensors and my car runs perfectly now. <whew>

Apparently failed sensors are particularly common for those that wash their engines. (There is a TSB out).

Monster231

Thanks Dave, I will give you a buzz early this week to see if we can hook up.

T_Vert

ill be in kentucky wed to sunday
dave