I have been trying to figure out my idle problem all week. I just replaced my timing belt this past weekend. I have had it apart twice now to verify that I have all the timing marks lined up correctly. The truck runs just fine it is just the idle takes time to drop between each shift and when I come to a stop it idles about 1100 RPMs. I have cleaned the connectors and put dielectric grease on the IAC, TPS, and MAF. I still have the same issue. I also took the IAC valve out and cleaned it. I checked the resistance in it and reads 10ohms. I was going to try to check the voltage on the wire but I can't get my leads into it. I will have to try some wires then touch my leads to it. I can start my truck and unplug the IAC and it does nothing to the idle. I can unplug the MAF and it about stalls. I have a check engine light on with P1506 = Idle Air Contol System Over Speed Error. Should I replace the IAC? I am not sure what the sympthoms of a bad IAC are. Also, the week before I replace the timing belt my check engine light came on with the P1506 but it went away. Thanks in advance.

 

Vacuum leak.

 

I did try to do a vacuum leak test but I am not sure if I did it right. I just used some carb cleaner and was spraying it on some of the vacuum lines. I thought I read somewhere to unplug the TPS and then try but I did not try that yet. What is the correct method? Also, I have replaced the PCV since I did not know when the last time it had been replaced.

 

How many miles on your truck?

I had a problem of high idle on my 2.3 l '91 Ranger for a long time. Everyone said I had a vacuum leak some where. Hunted all over and never found one. At about 100 k miles, I replaced the spark plugs. To make the job easier, I removed the upper intake manifold. At that point, I discovered that the whole intake system (throttle body and Intake manifold) was cruddy on the inside. Using a plastic safe cleaner, I went to work on cleaning the whole system. There was a build-up of carbon on the edge of the throttle plate . Got the throttle body and throttle plate squeaky clean, put everything back together and no more high idle problem. The truck ran better that it ever did from the time I bought it (58 k miles).

Its at least worth a look.

Let us know what you find out.

 

Thanks for the suggestion. I have 165000 on it. I replaced the plugs and wires about 10000 miles ago. That was the last time I cleaned the throttle body as well. I didn't take apart the intake though. I also have fuel filter for it. I had trouble getting the old on off so I haven't replaced it yet. I will thoroughly clean the throttle body tomorrow and try to change the fuel filter then post back.