Unusual RPM situation
 

Hey guys.

Have a problem with my 96 C1500 with 4.3L 5 spd MT

Some background.

I bought this truck a year ago, and it has been a pretty good reliable truck but since the day I bought it, (used with 185k miles) I noticed that the rpms will not drop to idle unless the truck is stopped, or under 2 to 3 mph. If im decelerating, they stay around 1300 to 1600 even when the clutch is in and the shifter in neutral. Does this when cold or hot.

Just drove it to california and back to salt lake and still did it after hours of driving. (developed a bit of an electrical issue too, but that's a problem for a different post)

Ive cleaned the throttle body, checked for vacuum leaks, and checked the accel cables (pedal and cruise control)

Im at a little bit of a loss as to what to check from here on out...

Any suggestions?

Re: Unusual RPM situation
 

Check your Idle Air Control valve.

Re: Unusual RPM situation
 

I have somewhat the same situation, have for years. I will shift into neutral when exiting the interstate and glide down the ramp before coming to a stop. The truck will drop to about 1000 rpm and then quickly drop to 700 at stop. I have replaced the IAC valve, with no change. I also replaced the throttle position sensor, twice. I gave up thinking that's the way it is supposed to be. My truck is a 1996 GMC K1500, 350 with manual transmission. Kind of funny same year and manual transmissions.

Re: Unusual RPM situation
 

The 1000rpm is normal when coasting, keeps power accessories working properly including steering and brakes.

Re: Unusual RPM situation
 

I haven't seen anyone mention the pressure switch on the power steering pump. In turning situations the switch actuates the rpm response so the engine doesn't die out or drop too far to kill the engine. Even the 7.4L engine in my K2500 has this pressure switch.

Re: Unusual RPM situation
 

I did not know that there is a pressure switch on the power steering pump. In my case I recently replaced the power steering pump and hoses. I went from a very minor leak on the pump to dumping half the power steering fluid.

OutlawDrifter, thanks for the comment. I figured it was something like that. I have an old Xterra and when I coast, it drops back to idle instantly. Different designs between the two makers.

Re: Unusual RPM situation
 

Are you referring to the EVO system? That's for reduced steering effort at low speed, so soccer moms can steer their Suburbans in the parking lot :lol:

His pickup is a '96 and I believe EVO wasn't available until 1997.

Re: Unusual RPM situation
 

That is correct my 1996 does not have EVO.

Re: Unusual RPM situation
 

That might describe the system on my '97 K2500 since it's a much heavier truck than my '89. I'm referring to the system in smaller engines in vehicles that drop rpm's in tight turning situations and keep the engine from dying due to the drag from the accessories like alt. and PS.

Re: Unusual RPM situation
 

To my knowledge, none of the GMT400's have anything like that. The EVO system was the only one that had a sensor, and it just increases the pressure in low speed situations.

I'm not saying it doesn't exist, I've never ran across one, and I've had everything from 4.3L/5 speed W/T trim pickups to my 1999 K2500 454 'burb.

Re: Unusual RPM situation
 

This is what the pressure sensor looks like. It has an offset adapter for the hose instead of a straight fitting.

Re: Unusual RPM situation
 

That's the EVO sensor.

Re: Unusual RPM situation
 

It's a pressure sensor, and it's from a 92.

Re: Unusual RPM situation
 

A 1992 what? Not saying your wrong, I've never seen one that wasn't for the EVO system on a GMT400 pickup or SUV.

Re: Unusual RPM situation
 

I was just showing what the sensor looks like in case his truck has one. I'm not saying you're wrong either. That one is from a 92 Cadillac Sedan Deville.

Re: Unusual RPM situation
 

No worries! Misunderstanding through the interwebs. I thought you were saying it came from a 1992 GMT400. I just was curious what pickup/SUV it was from.