Ok so I have a problem I can't figure out. The truck accelerated and travels fine BUT when its idle and in gear (stopped at stop light) it will try to stall momentarily or feel like it's missing every 10 seconds or so. When I hit the gas and start driving it runs normally. Lately when it does this I notice the speedometer jumps up to 10-20mph (but truck is not moving at all) then when it stops trying to stall the speedometer goes back to zero.

We recently had a shop put a new distributor on the truck because it went out. This current issue was happening before the distributor died. When I got it home I replaced the spark plugs,wires and coil. But non of that fixed the problem.

I'm not sure what to look at as the cause. Could this be a sensor issue?

1993 suburban 350 RWD

 

Speedo jumping around is probably not related to your idle problem - likely two different things.

on your idle, first thing I’d check is fuel pressure. Low or marginal fuel pressure can cause a lot of funny problems. Here is link on how https://www.chevytalk.org/fusionbb/s...php?tid/253427
I had similar poor idle and fuel pressure was marginal. Replacing pump with ACDelco fixed it as well as gave truck a lot more power in normal driving. Make sure you check fuel pressure when blipping throttle and ensure it’s not dipping under higher fuel demand. Mine was ok at idle but dropped when hitting throttle. Also recommend checking after fuel filter - a lot easier to release fuel lines from retainers to get space for adaptor.

as for speedo jumping. I had issue where speedo would jump with rpm. I could rev engine in park and get speedo to move. Replacing inductive sensor in transmission fixed it. Evidentially signal was weak on old one and though it worked, it must have been low enough signal that noise was causing problems.

 

i would check your grounds. the speedo jumping around might be due to some sort of electrical feedback and this could also be effecting how the computer reads your sensors