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1993 Ford Ranger 3.0 Sticking Throttle

I have a manual 1993 Ford Ranger 3.0L Super Cab with 96,000 miles. I don?t drive it much more than 10 miles a day and only on surface roads. Starting probably about 10 months ago, after I drove on the highway for 20 to 30 minutes, the throttle would stick if I put truck in neutral. (I typically don?t use the engine to break, so when I take my foot off the gas I typically push the clutch in, take it out of gear, let the clutch out, and come to a stop with the truck in neutral). However, once the sticking throttle issue starts, the engine will rev up quite a bit anytime the transmission is in neutral. It won?t come back down until after I?m almost at a complete stop. Then when the light turns green, and I begin to accelerate, I need to change gears rather quickly (because the throttle starts to stick again) or risk burning the clutch and/or slamming the gears. My guess is that when the ?something? heats up enough it expands and causes this problem. I thought I might be able to solve this problem by cleaning the throttle body but either I didn?t do a very good job (quite possible) or that wasn?t the trick. Since I don?t drive on the highway, or very far every day, I wasn?t too worried about it. Now, the problem is starting to occur during my normal daily drive and is guaranteed to happen anytime I drive over 55 mph for 20 min. My temporary solution is to down shift and keep the transmission in gear until I?m almost stopped but this wears on my clutch more than I?d like.

Has anyone else had this problem or recognize its symptoms? Does anyone have some ideas I could try? Thanks a bunch!

Have you ruled out a sticking throttle cable?

Assuming the cable is not the problem, idle speed is controlled by the Idle Air Control (IAC) valve. If the IAC valve is dirty or sticking it can cause incorrect idle speed.

Is the engine warming up quickly and getting to normal operating temperature? If the engine is running too cool the computer will increase idle speed.

I haven’t ruled out the throttle cable…I’ll look into that and the IAC. I hear what your saying re: the increased idle speed. The engine doesn’t warm up quickly and the super high reving doesn’t happen until after the engine is warm. If it’s something sticking, why will it only slowly come back down after I’m almost stopped?

There is a return spring on the throttle plate, to close the throttle when you lift your foot off the pedal. When you cleaned the throttle body, did you clean the pivot points for the throttle plate? If the plate is hanging up it might be causing your problem. The return spring might be slowly closing a sticking throttle plate.

If the engine doesn’t warm up quickly you might want to install a new thermostat. If the thermostat is stuck open the engine will warm slowly and may not reach correct operating temperature. An engine running below correct temperature wastes gas.

Good call on the hinges. I check on that too. The engine warms up really in about 60 seconds. I usually let it sit there and idle until the rpms come back down. Could the spring get weak when heated and not be able to overcome the grime on the pivot points?

So I cleaned everything again (not much there really). The hinges are clear, the springs seem ok, the pedal responded very well to the throttle and vice versa. Do you think there could still be something mechanical going on here?

I looked at the IAC solenoid, disconnected it while the engine was running and the rpm’s dropped as expected. I also checked the Throttle Position Sensor (TPS) with a DMM and it read 5 V when the engine was off and 3.47 K-ohms which is also as expected. I also started the engine with the TPS disconnected and the RPMs were low and sporatic also as expected. I got all of these ideas and expectations from the Haynes Repair Manual. So I think the TPS and IAC are also ok (I suppose if they weren’t I’d also get a check engine light). I guess the next thing to do is take her back on the highway and see what happens? Then maybe I could pull off if/once my rpm issue starts happening again, open the hood, and try and see what the problem is? What do you think?