Hello, I'm new to the forum and have a ?? about my 1998 4.2 V6. I purchased the truck 4 years ago with 100,000. The truck now has 151,000 and does not use a drop of oil between oil changes(Valvoline semi-synthetic), makes more power than ever and I'm getting the best gas mileage ever.
At 130,000 miles I replaced the original sparkplugs with AC/Delco Rapidfires.The problem is the truck developed a rough start when cold. After the motor starts it runs perfectly! 5,000 miles later I got a check engine light and a computer code for multiple cylinder misfire. The motor would buck everynow and then on a sight uphill grade at highway speeds, i thought the lock-up torque converter was kicking in and out since the trans. had so many miles. I switched to Bosch platinum plugs and no longer have the bucking misfire but still have the cold start issue.
Now the temp. is near zero here in Iowa and the motor cranks roughly for 6 or seven seconds before starting(but runs great after starting) and never fails to start.
Any ideas or experience with solving this same problem would be greatly appreciated . I think I will also go ahead and replace the original sparkplug wires. I wish I had just left the original plugs in the motor, and after 130,000 miles the original plugs still looked good. Thanks, Pete

 

When was the last time you cleaned or replaced the IAC valve, Fuel Filter, MAF sensor?

Regards

Jean Marc Chartier

 

I replced the fuel filter at 100,000 (probably due again). I'm not sure what a IAC is?? is it something you clean or replace??

 

nitro,

Sorry I should have been more explicit. IAC is the acronym for Idle Air Control. It is a valve that allows air to bypass the closed butterfly in the throttle body at idle. The PCM, powertrain control module, controls this valve to help regulate the idle. During operation carbon soot accumulates in the valve. It gets rubbed off as the valve moves. When cold weather sets in the valve tries to move into a position that it was not using during the warm weather that is covered with soot. The valve gets stuck and the PCM has trouble controlling the idle and it gets rough.

The MAF is the Mass Air Flow sensor. It measures the incoming air volume. It has two wires that get dirty over time. Windex and Q-Tips can be used to clean the wires.

JMC

 

nitro,

The IAC is #2


EDIT:

I forgot to mention plug wires. I would have a look at them too. Spray some water on them at night with the engine running. If you see sparks change the wires.

JMC

 

Thanks for the great tips!! I will give them a try this weekend. Thanks, Pete

 

Awesome diagram with IAC, can anyone point out where the MAF sensor is? I have 76000 miles on my '98 4.2, I would like to check it out.

Dan

 

Remove your air filter and it should be behind it.

JMC

 

Where can I get diagrams like that?