Troubleshooting - Engine Won't Decrease Rpms When I Shift

[goneboy87]

My mechanic hasn't been able to figure out what's going on, so hopefully someone here has an idea:

I drive a 1997 GMC Sierra 1500.

4x4

5.0L Engine

5-speed stick

 

The engine doesn't drop in RPMs after you let off the gas as quickly as others with the same engine, or even as quickly as it used to in my truck. If you're going down the highway and put it into neutral without using the clutch, the RPMs don't drop at all. If you use the clutch, the engine will very slowly drop in RPMs, but it still won't decrease to below 1500 RPMs (until you release the clutch, where it will match the speed of the transmission).

 

Also, when the engine is cold, it hesitates like the spark is retarded when I step on the gas.

 

I get an intermittent check engine light with code P0420.

 

Has anyone had experiences like this?

[georgecdisc]

My mechanic hasn't been able to figure out what's going on, so hopefully someone here has an idea:

I drive a 1997 GMC Sierra 1500.

4x4

5.0L Engine

5-speed stick

 

The engine doesn't drop in RPMs after you let off the gas as quickly as others with the same engine, or even as quickly as it used to in my truck. If you're going down the highway and put it into neutral without using the clutch, the RPMs don't drop at all. If you use the clutch, the engine will very slowly drop in RPMs, but it still won't decrease to below 1500 RPMs (until you release the clutch, where it will match the speed of the transmission).

 

Also, when the engine is cold, it hesitates like the spark is retarded when I step on the gas.

 

I get an intermittent check engine light with code P0420.

 

Has anyone had experiences like this?

I had the RPM issue with my '98 5.0 5-speed. I adjusted the set screw on the throttle cable near the intake. This screw sets the idle for the throttle, and with it slightly in too much it would cause RPMs to not drop. Make sure not to unscrew it too much, because you will be able to feel the slop in the gas pedal every time you put your foot back on. Hope this solution works for you.

 

P0420 looks like an o2 sensor problem. Might just need to replace it.