Idle is surging when going down hill

[rocklaurence]

Lately, when Im coasting the engine will surge (RPM will increase and then decrease). This only happens with no pressure on the gas peddle and the truck is coasting (going down hill or approaching a stop). Is it the throttle plate not closing, idle solenoid? Could it be due to less back pressure from a "High Flow" cat? As my bio states, it is not an OEM motor.

 

[TSTONE]

Have you ever replaced your tps? If not it could be your problem and it's a cheap part to try.

 

[Rhett]

Lately, when Im coasting the engine will surge (RPM will increase and then decrease). This only happens with no pressure on the gas peddle and the truck is coasting (going down hill or approaching a stop). Is it the throttle plate not closing, idle solenoid? Could it be due to less back pressure from a "High Flow" cat? As my bio states, it is not an OEM motor.

Make sure you don't have any vacuum leaks. Check all of the hoses, manifold seals, intake tube seals.

Oh...I just noticed you run an aftermarket cam...I don't know about that cam, and how it would affect idle.

Could be the throttle plate gummed up; could be a vac leak somewhere;
could be something with that cam, but to me it seems like if it was the cam then you would notice a loping idle all the time.

 

[rocklaurence]

It didnt do it for the 1st 18 months after the rebuild. So, its something new. Its a steady/repeditive surging until the truck slows down. Could it be that my torque converter isnt unlocking?

 

[cfkane]

Is there any evidence of deposits on the intake side? High levels can act as a fuel “spongeâ€￾ that release the fuel under vacuum. This can cause the O2 sensors to oscillate with a resulting idle fluctuation. For about $20 and a tankful of gas a good PEA additive will clean the engine without any harmful effects.

 

[rocklaurence]

Thanks, I'll check for vaacum leaks and maybe run some cleaner through @ the manifold vaacum fitting. After the Hurricane passes.

 

[cfkane]

Best of luck on the storm. BG 44K and Chevron Techron are two very good additive packages.

 

[rocklaurence]

I MAY HAVE FOUND THE PROBLEM. THE THROTTLE CABLE OUTSIDE SHEETH IS ROTTED THROUGH. Maybe its preventing the throttle from closing when I take my foot off the accelrator. Hmmm?

 

[Billy177]

before i had my tranny rebuilt mine would do that unless i had overdrive off