I have 99 blazer that runs & idles fine my problem is at 1500 rpm it stays there unless i brake almost to stop then it will idle at 650.i checked for vac leaks none,cleaned the maf tb & egr. Replaced the iac & tps .The code i keep getting is p0507.Two months ago i changed the plugs dis wires cap & rotor ,fuel filter & air filter.Yesterday i disconncted the maf sensor & did not notice any change at all if the maf was good wont there be some kind of change? Thanks Jim

 

Yeah: I have been lately experiencing high-rev starts(cold or hot)I looked at the usual suspects:IAC,MAF,vacuum etc. NO codes and a week later all is fine again,so maybe my cleaning the MAF did it! But it did NOT return to normal immediately! The only factor I can see is the change in vehicle usage:from 125 hi-speed miles a day to 3-4 miles a day with only one high speed blast a week...What say you folks? LMK!
97 4.3 187K

 

Was the truck doing this before the tune up? What brand did you use for the tune up?

 

P0506/P0507 - Idle Control System RPM Lower/Higher Than Expected

see if this helps

 

Yes .. And every thing was ac delco...

 

Yeah I believe there should be a noticeable change when you unplug the MAF, so that is a possibility. Also does it act any differently with the air conditioning on?

 

I dont notice any difference with it disconnected. The ac dosent work.

 

So it DOESNT idle fine. But is this in the driveway or like coming off the freeway?If there's no change apparent when you disconnect the MAF it means all the key air Fuel sensors are working. Esp the MAP.
If it runs better, almost always MAF, if it runs worse often the MAP.

You say it does idle right at stop signs, while brake is on, I assume. What happens when you let off brake?

What happens when you are in driveway? If you rev it past 1500, does it settle to 650 in a second or two? Press and let off brake?

Check both PCV lines. From engine to intake tube and intake maniflod to valve cover. Make sure pcv rattles.

Clean throttle body and plate.

Pull and clean EGR. {Yeah, long shot since it doesnt stutter on acceleration but could be}

 

When i first startup it revs to 2ooo but comes right down to 9000 till it warms up .Once warm i can rev it up & it will drop to 750. In gear it will stay at 650
on the road when i come off the gas it wants to coast at 1500 .but when i stop at signs it will idle at 650 & stay there.

 

I know I threw a lot out there. I am not asking you any questions that I wouldnt check myself if I had that problem. And I have had it.

But when you let off the brake, does it stay at 650. If you then put it in neutral at that stop sign, does it stay at 650... or rev higher?