Yesterday, the engine was racing as soon as it started and no way to slow it down. The throttle is remaining closed, but the injectors are pouring the gas to it. So, it is not any cable, solenoid or speed control causing the problem. The computer codes were: E26, E27, E48 and F46
So, that told me that there is an EGR problem and a Throttle position sensor problem. I purchased a new Throttle Position Sensor, installed it and there is only a slight decrease in engine RPM. I cleared the codes in the computer and now it doesn't show any codes. I don't dare run it too long because it seems to be running about 2000 to 3000 RPM. I haven't tried to measure it, so I'm guessing. I don't know how long I would have to run the car in order for the computer to record any new codes. What else could be causing this problem?
Help!
TIA,
Joe

The injectors can pour all the gas they want into the car, but if it is not getting any air, it will not run. Either your throttle is no closing completely to idle or there is a vacuum leak somewhere that is supplying intake air.

Thanks for the reply, Ranger. The butterflies did appear like they were not quite closed all the way, but they were very close to closed. I was troubleshooting with the cleaner off and could see them. The throttle linkage was up against the soleonoid that controls the idle speed. Since none of this has been adjusted, I am assuming that it is correct. Is that a bad assumption?

I hate to give any advice on an '88 because I am just not sure if it has an ISC motor like the 4.9 does or not. I would start by using some carb cleaner, hold the throttle open (engine off) and clean it out good. Have someone turn the key off while you are watching the throttle blade (butterfly) and see if it drops closed a lot after key off. That should tell you whether it is held open by carbon or ISC.

Thanks again! I'll try that today. I was wondering if the bad TPS could have caused the ECM to fail. What do you think about that?

Not sure, but I don't think so.

Ranger, I have news! I discovered that I do have a ISC motor and it is the cause of the trouble. Yesterday, I backed off the nuts that hold it and I was able to get a nearly normal idle. Then I increased engine RPM and watched the plunger retract on the ISC. I disconnected the ISC connector and shut the car off. I then re-mounted the ISC and hooked up the connector to it. I disconnected the battery and waited about 5 minutes. I then hooked up the battery and started the car. :confused: It went back to the high idle speed. The ISC motor extended its plunger. What is the trick? I figured it would re-learn the idle speed if I did all of this, but it didn't happen. I no longer have any coded stored in the computer.

Thanks!
Joe

This sounds like the TPS. You can't just slap a new one in there, it might not be calibrated. Go into diagnostics, then press LO and then press HI once. This should put you at parameter 0.1, which is the calculated throttle angle. Hold the throttle arm open a little, then push against the ISC plunger. It should retract all the way. Unplug it while it's retracted to keep it there. Let go of the throttle arm. With the engine warmed up, it should still be running around 450 RPM. If it's not, you need to adjust the minimum air screw on the throttle body (you can see the throttle arm resting against it, unless the 88 is different from my 90, but should be similar since they're both 4.5). Once it's idling at 450 with the motor retracted, look at P 0.1. It should be close to 0, and if it is not within 1.0 either way, then you need to adjust the TPS. Loosen the two torx screws on it and rotate it until it reads as close to 0 as possible. Then you can do the idle learn procedure.

Ranger, I have news! I discovered that I do have a ISC motor and it is the cause of the trouble. Yesterday, I backed off the nuts that hold it and I was able to get a nearly normal idle. Then I increased engine RPM and watched the plunger retract on the ISC. I disconnected the ISC connector and shut the car off. I then re-mounted the ISC and hooked up the connector to it. I disconnected the battery and waited about 5 minutes. I then hooked up the battery and started the car. :confused: It went back to the high idle speed. The ISC motor extended its plunger. What is the trick? I figured it would re-learn the idle speed if I did all of this, but it didn't happen. I no longer have any coded stored in the computer.

Thanks!
Joe
Put pressure on the ISC plunger with your thumb til it fully retracts, the pull the electrical connector. Now adjust the plunger to a .030 gap to the throttle linkage. Reconnect the electrical connector.

Thanks Ranger. I'll try that this morning.

Duh! What a dummy I am! The codes said a shorted throttle position switch. I read throttle position sensor. Not the case. The Idle Speed Control motor has a position switch inside it. It notes when the plunger is fully retracted. My switch remained closed regardless of the position of the plunger. I got a new ISC motor and everything worked great! Problem solved!

As long as I'm here asking questions, where the heck is the ding-a-ling? My Mom calls it the "ding", but I'm talking about the JC Penny's sounding chime that is supposed to sound if you leave your keys iiin the ignition or leave the lights on. I cannot find that module to save my butt! Today, I was staaanding on my head under the dash looking for that thing, but I cannot find it. Can anyone tell me how to find it?

Thanks,
Joe