strange idle problem...need suggestions

[69MyWay]

My 85 is running pretty darn good.

However, it will get into a strange idle speed loop that will cause it to surge hard, and stall if you don't raise the idle a bit with the throttle.

This makes bumper to bumper traffic a bit tricky.

Here is the strange thing. The majority of the time, it is just fine. When it goes into these loping cycles, the idle speed will surge 500 plus RPM up and down. When it dips below 500 it will stall. This is in or out of gear.

For giggles and grins, I unpluged the IAC. It continued to lope. This confused me, because I thought the IAC was the main factor in the idle control.

I reached down and bumped the TPS with my thumb and it cleared right out, but I also brought the idle over 1,000 RPM by doing that.

My scanner shows me lean at idle off the newly installed three wire O2. It did this with the one wire O2 as well.

I do believe I have at least one funky injector, because I have heard it hissing and dripping fuel in the intake after shutting the engine off once or twice. It is also still hard to start after it sits for more than a day (not terribly hard to start...just not as quick as when it has been running).

I have replaced the fuel pump, regulator...and it has a fresh tune up on all the usual goodies.

Thoughts?

 

[8388]

For giggles and grins, I unpluged the IAC. It continued to lope. This confused me, because I thought the IAC was the main factor in the idle control.

This would indicate that the throttle blades are opened a bit too much.

Remember, the ecm is constantly trying to reach the correct values.

I would look at these thing first:
Make sure the tps is set right.
make sure the IAC has been reset.
make sure the throttle blades are not sticking.

 

[geekinavette]

Re: Re: strange idle problem...need suggestions

Remember, the ecm is constantly trying to reach the correct values.

But...he said that he unplugged the IAC, which is what the ECM would use to try to correct the idle, so that factor is out of the equation. Right?

Sounds like you need to hunt down what you feel is a faulty injector. How does the plug for that cylinder look compared to the others?

Bill

 

[ejrempel]

Is your fuel filter clean?

 

[69MyWay]

fuel filter does need replacement.


I have not pulled each plug.......yet.


I am not going to be able until my shoulder heels up a bit

 

[-=Jeff=-]

I would change the Fuel filter and also Set minimum air. I am thining the TB Blades are not set correctly..


Or, it could just be the loose nut behind the wheel.. LOL j/k