whats up guys, just picked up an 94 suburban with the 7.4l.

Im having a issue with it. When i put it in drive and let off the brakes, the truck will coast up to 20 mph by itself and also shift in to second gear.

It also sounds like the idle is a little high too.


no matter how warmed up or cold it is, truck will always do it.

any one have any ideas?

i was thinking timing may be off?


thanks

 

Welcome to the forum.

Did it do it when you got it or start afterwards?

 

does it have a tach? how hgh is the idle? sometimes a sticky throttle plate and make the idle high and all those related symptoms.

 

thanks for the responses.


Yes it has done it since i got it 4 days ago.


and no no tachometer. im going to estimate it idles at around 1500 2000 rpms


i was also thinking maybe its the idle air control valve


but you think the throttle plate huh. how should i go about checking that.

i work on VW's and know all those car symtoms and problems hahah


thanks guys

 

VW? Yea, I m sorry to hear that. I know a good therapist if you need one.

Ok, well, take off the idle speed control solenoid and see if its gunked up. Carb cleaner works good for that and the throttle plate. Do a Engine off Key on voltage test on the TPS sensor as you WOT it a couple of times. Look for a dropout in the range(remember they only go from 0.5-4.5v). I had a problem a while ago that when the car was hot the TPS would send the wrong signals and give me a high idle all the time, even on the highway. Same thing for the Engine Coolant Temp sensor(but check for resistance)...Test when Hot. They will give you the weird signals that way.

Then check and make sure the battery and alternator arent weak. Something about the weak battery put the alternator into high output boosting idle to meet the charging demand. I dont know why though. But in these GM cars when the battery is weak, the car will idle high.

Clutch fan=check it.

The coasting and upshift is because the idle is too high

 

thanks for the help so far i just replaced the idle air sensor and it seems to be doing ok for now

as you said with the battery i think they may have to do with it too seems like the battery is weak guage shows low voltage, so i may just swap out the batter see if that helps because the alternator is new and the battery is old ha


thanks man