1994 Ford F-250 Engine Light and Idle Problem

My 1994 Ford F-250 with a 5.8 Gas engine refuses to idle below 1500rpm. Is this a common problem in older engines and what might be causing the problem? I have a 15gpm hydraulic pump attached on a clutch pump, but the over revving is a fairly recent problem.

I’d first check for any vacuum leaks that might be causing a high idle. Also try a good cleaning of the throttle body of carbon. Is the check engine light on at all?

Yes to the check engine light, though not every day. Also a recent occurrence but both did not occur at the same time.

I’d definitely get it scanned. Knowing the trouble code will probably help in diagnosing the high idle. You could have a bad throttle position sensor or something related.

Agreed. Would the diameter of the main vacuum line affect the vacuum pressure? That seemed to be the start of the high idle situation. The replacement line was not an exact match.

It should not make a difference unless it affects the way it fits, such as causing a leak.

Many thanks ProTech. Can I ask an unrelated question?


What do you call the idler on the upper left ( as you face the engine) side of a GMC v8 Vortec engine. I need to replace one.

What year and what size V8?

2006 6.0L GMC Sierra 3500 series.

OK, as you face the engine, the uppermost left pulley is called the tensioner. It keeps the tension on the belt as it rotates. It’s very easy to replace.

Agreed. Auto parts store would recognize it as a ” tensioner” pulley or is there a specific name? Have replaced similar tensioners on my ’94 Ford.

yes, you just need to ask for a belt tensioner and they should know what you mean. Make sure you say the ‘main’ drive belt tensioner, as there is another smaller belt and separate tensioner for the A/C compressor.

Many thanks. Do you know if the pulley and bearing come as a separate part of the assembly or do I need to replace the whole thing?

It will come as a complete unit, not in separate pieces.