I have a 1996 Blazer LS with a 4.3 A/T 4WD, and I have just recently had a problem with engine rpm's "surging" while i'm coasting around 30 - 40 mph. Generally at a speed of 35 mph my rpm's are around 1,200, and if I let off the gas completely, the rpm's will decrease by about 200 - 300 (depending on speed) then go right back. This happens almost every other second. Also (on a side note) engine temperature does not have any effect on this condition. Any help with this problem would be greatly appreciated.

- Blazer Buddy

 

Does this happen during a particular outside temp range?
Dos this happen if your heat-a/c controls are off?
Are you getting a CEL "Check engine light"?

My initial thought is a failing IAC (Idle air control) or TPS (trottle position sensor)

What kind of voltage is on your volt gauge while this is happening?

'96 you say. You running a AC Delco battery, like this is the second one and its around 4 years old?

Got any headlight dimming?

Sorry for all the questions, just trying to rule out a few things.

By teh way, welcome to teh site.

 

The temperature has no effect on the problem, no heat or a/c controls are on, and I have no SES light on(Service Engine Soon). I'm getting a reading of 14 volts (problem does not effect volts). No headlght dimming, and I am running an AC Delco battery but its only 2 years old. Thanks for the welcome and there's no problem with the questions, it was nescessary. Thanks Again.

 

Will RPMs be up there even at park/neutral?

 

Can you tell if its your torque converter locking-unlocking, or if its shifting between 3rd and 4th gears? Try driveing in 3rd gear and see if the problem goes away.

Have you checked your tranny fluid? Engine running after 20 minutes on level ground.