Problem with throttle/cruise control

[Marlin]

I have a 94 3/4t Chevy Suburban 2wd, has 191k miles. When the c/c is on and when going downhill the cruise will rev up and down even when on a slight downhill. Also it has started when just using the throttle with out c/c on. One has to apply then let off the throttle to maintain speed going downhill. Can't just let off just a little. Is it the throttle position sensor? FSD?

Thanks,
Marlin

[Marlin]

Any comments, ideas?

Marlin

[moondoggie]

Good Day!

Since your symptoms occur with & without the CC (cruise control) engaged, this would indicate the TPS (throttle position sensor) is NOT involved. Please forgive me if I'm being redundant, but there is no CC per se on your truck. (Go ahead, open the hood & try to point to the CC - it ain't there!) When you engage the CC, the 'puter ignores the TPS unless you push it down to override the CC to increase speed above where the CC is set.

I think any TPS problems would set a code. If memory serves, the TPS is three ganged potentiometers. The 'puter monitors to make sure they track each other, & a weird output from any one or two of the three will set a code.

I strongly doubt FSD involvement - this is not classic FSD symptoms. Of course, I've been wrong many times

[rjschoolcraft]

My 95 would do this when I first got it in 2000. A new injection pump under warranty cured that, and many other, problems. I don't know exactly what the issue was, I just know it was gone after IP replacement.

[HarrySanders]

I just posted about a pump replacement. Our only syptoms were SES light upon acceleration only and CC failure after engine was warm. It seemed to run fine otherwise. Could be the pump.

[ff43sc]

My truck also does the engine surging with the cruise on, I was first told it was APP(by gm mechanic..replaced it , still happening..) then told it was speed sensor in transfer case...replaced it still same problem,
On mine i can set cruise at 65 and on flat ground or any uphill at all, works great, as soon as decel happens rpms go from steady 2300 to 1800-2300, 1800-2300 in rapid succession....no other problems just an annoying happening....I saw another post about excessive play in speed sensor/tail shaft bearing..may cause this problem...any thoughts?

[TurboTony]

I've run into similar complaints of this condition before.

Usually an injection pump timing adjustment will cure it. Seems that if the pump is at the low end of the spec you will get a surge condition at some loads, usually light, part throttle type stuff.

Setting the pump to close to max spec will get rid of it.

Tony

[MTTwister]

Would slack in the timing chain have any impact?