engine stumble

[endless summer]

my 5.7 in my 98 stumbles sometimes at idle and low rpms. at higher rpms and highway speed there's no problem

 

[Schurkey]

All the usual questions:

What is the fuel pressure?

How old are the typical "tune-up" parts--cap, rotor, plug wires, spark plugs, O2 sensors, fuel filter, air filter, Distributor bushing and gear inspection, PCV inspection, EGR inspection, electronic timing advance inspection, evaporative emissions inspection, etc.?

Has the fuel injection "spider" ever been replaced? Does it still have poppet injectors, or has it been upgraded to the electronic injectors?

Connect a scan tool, look for "codes", but more important--verify ALL sensors and computer outputs.

 

[HotWheelsBurban]

If you have replaced the "tune-up" parts and everything else checks out good, it may be just the way the computer is set up. I've been dealing with this on my '97 350 crew cab, and that seems to be the consensus of opinion that the PCM may be changing the settings at idle or low RPM(especially when the engine is warm and the idling is extended) in an effort to extract maximum fuel economy. I haven't replaced the coil, plug wires or module yet, but I have replaced the plugs with the same # AC ones that were in it, and replaced the cap and rotor with the UMP vented unit, with brass contacts, and also the TPS and IACV. It was running better with the mid grade 89 octane gas, but today it's back to the goofy idle.

 

[Michael Salin]

Have you figu

my 5.7 in my 98 stumbles sometimes at idle and low rpms. at higher rpms and highway speed there's no proble

my 5.7 in my 98 stumbles sometimes at idle and low rpms. at higher rpms and highway speed there's no problem

Have you figured it out?