Hello all. I had posted a few weeks ago about a weird idle problem on start up, and it looks like I'm back again with yet another weird happening.

I've got a '92 s-10 blazer with a 4.3 TBI 2wd. Last night as I was leaving work a very strange thing happened. I was accelerating(in a parking lot so not very quickly), and before I knew it the car starts accelerating like no other.... The brake was so stiff I could barely press it, and it took a pretty massive amount of force to get the truck to stop. As soon as it stopped moving the engine was still trying to accelerate so i put it into park.... and as soon as I put it into park the RPM shot up again past 3000. The only way I was able to get it to stop was to turn the car off and back on.... after I did this the car was totally fine the rest of the drive home. I've gone through all the flukes I can think of(cruise control, pedal getting stuck on floor mat, hitting accelerator rather than break...), but none of these ideas have worked as the CC was off, the floor mats weren't in the way, and the only way I could have stopped the car was with the break... so the accelerator idea is out. Also, I tried to take it out again today for a small test drive around the neighborhood, and it did it again, just once and when i turn the car back on its back to normal.

Has anyone had a problem like this or have any idea what the problem could be?

 

its haunted. its like the movie carrie.....except its out to get you.

haha jk!

my truck does that too sometimes. let it warm up a bit before you drive off.

did it have a high idle when you started it that time?

 

The part about the brake pedal being hard to operate makes me think there is a vacumn leak problem involved, and it so happens that another member had a sudden rpm increase situation. Here's the thread, and it turned out to be a hard to find vacumn leak causing his problem. There may be no connection with your problem, but read and see what you think.

 

That actually looks to be very helpful. I'll give it another read through in the morning and try and test it at some point during the day. Thanks for the help and if I get it fixed I'll be sure to post again with what did it.

 

Rather than start a new thread, I thought I'd state my problem here due to the similarities. A few days ago I changed my spark plugs, wires, and oil in hopes of getting a smoother idle/acceleration. It didn't work. There is a slight sputter during idle and after I let off the pedal coupled with a rattling/jingling sound. I removed the intake and cleaned the throttle plate with Valvoline carb and throttle cleaner. I removed a small amount of carbon gunk around where the plate seals, but it didn't help. The I took it for a drive and realised it was capable of driving itself. I went around the parking lot three times without touching the accelerator. The pedal is not stuck and the throttle cable is loose. It's a 93 S10 4.3 W. Any advice would be great. The brakes are fine and I have normal power.

 

Scott, when you cleaned the throttle body did you remove the IAC valve and clean the bore? If the throttle isn't hanging up, there are only two explainations. #1 - Vacuum Leak & #2 - IAC valve not functioning properly.

 

its haunted. its like the movie carrie.....except its out to get you.

Brandon did you mean the movie Christine????? The 1958 plymouth that killed people....

 

No I didn't. I need an engine anatomy lesson.

 

The IAC valve is located on the upper intake plenum above the throttle blade. That would be one place to clean and see what happens. It is possible that the IAC valve has gone bad, but clean it first. Once you have cleaned it, if things do not improve, inspect all vacuum lines for a leak.


Here's a picture.

[IMG]local://upfiles/667/30F012E8731F48D5BB4406CD94FBF9F2.gif[/IMG]

 

Thank you. I'll post the results after I clean it.

EDIT:

Do vacuum leaksalways/most often result in loss of braking power?

EDIT #2:

I removed and cleaned the IAC, but it didn't make a difference. It still rattles and sputters at idle and can maintain 5mph on its own on a level surface.