88 ranger intermittant idle

I have a 88 Ranger V6 2.9L automatic that idles high in park(1600RPM) and in drive(1200RPM). Sometimes revving the engine will cause the idle to come down to normal operation, but this trick does not. What is strange about is the fact that it will return to normal idle speeds(park 1000RPM, drive 850RPM) without notice or warning. It can happen whether it has been run or turned off for a short period of time or long period of time. I have replaced the spark plugs, idle control sensor, and throttle control sensor.

Could this be a vacuum leak, another sensor, or something else? Any advice would be appreciated.

Thanks

I also had an 88 Ranger (GT) with the same problem. I don't suspect a vacuum leak, because if there was a leak, the problem wouldn't disappear. I would suspect a bad idle control motor, throttle position sensor, or coolant temp. sensor. When you say idle control sensor, you mean idle control motor i hope. The first thing the check is the throttle valve bore. A lot of times they can get a piece of carbon or other foreign material caught in between the butterfly and the bore. Pull the air intake tube off the engine, and visually inspect the inside of the throttle body to make sure there isn't any carbon buildup(It will be nasty, a cleaning with carb cleaner and a rag should help it, anyway..). If this doesn't improve, inspect the idle control motor air passages for carbon buildup. Now would be a good time to test your throttle position sensor, coolant temp sensor, MAP sensor and EGR valve and sensor. Refer to a good Haynes or Chilton manual for testing procedures and sensor specifications.

+1

It does seem like an issue with the IAC (or Idle Control Motor). Though, you need to make sure that is the problem before blindly replacing it. There's nothing like buying a part, installing it, and the problem is still there :).

Pete

Thanks for the advise. I figured to start with the most obvious and cheapest first: inspecting the throttle valvle bore. After taking it apart and cleaning it out throuroughly, the high idle problem is still there. Actually, the bore was pretty clean. I'll check the idle control motor next.

As for the idle control sensor, I wasn't referring to the motor but the black sensor box that is mounted on the rear of the engine wall to the right of the throttle body. I thought that was the name of it but escapes me right now. The truck idle was spiking before and replacing that sensor corrected the spiking.


I also had an 88 Ranger (GT) with the same problem. I don't suspect a vacuum leak, because if there was a leak, the problem wouldn't disappear. I would suspect a bad idle control motor, throttle position sensor, or coolant temp. sensor. When you say idle control sensor, you mean idle control motor i hope. The first thing the check is the throttle valve bore. A lot of times they can get a piece of carbon or other foreign material caught in between the butterfly and the bore. Pull the air intake tube off the engine, and visually inspect the inside of the throttle body to make sure there isn't any carbon buildup(It will be nasty, a cleaning with carb cleaner and a rag should help it, anyway..). If this doesn't improve, inspect the idle control motor air passages for carbon buildup. Now would be a good time to test your throttle position sensor, coolant temp sensor, MAP sensor and EGR valve and sensor. Refer to a good Haynes or Chilton manual for testing procedures and sensor specifications.

Actually, the idle control sensor that I was referring to is the MAP sensor.



Thanks for the advise. I figured to start with the most obvious and cheapest first: inspecting the throttle valvle bore. After taking it apart and cleaning it out throuroughly, the high idle problem is still there. Actually, the bore was pretty clean. I'll check the idle control motor next.

As for the idle control sensor, I wasn't referring to the motor but the black sensor box that is mounted on the rear of the engine wall to the right of the throttle body. I thought that was the name of it but escapes me right now. The truck idle was spiking before and replacing that sensor corrected the spiking.

Take a 3 lb. hammer and tap your throttle body. It is a small piece of dirt in the valve. This is still common on Mazda and Ranger engines. Tap it don't hit it hard or it will crack. Sounds dumb but it works.

I've heard of people doing that with the engine lightly revved. The idle control is mounted on the pass. side of the intake(top), wiring plug facing cab.

Gave this a try without any change, unfortunately. Although it sounded logical. Decided what the heck and replaced the Idle control sensor again. What a difference it made! It appears that the current ICS, was bad and its first replacement was bad as well. The second replacement was finally the winner and corrected the high idle.

Thanks for the ideas and assistance!


I've heard of people doing that with the engine lightly revved. The idle control is mounted on the pass. side of the intake(top), wiring plug facing cab.