Our Community is 940,000 Strong. Join Us.


97 Blazer code PO507 replaced IAC still high rpm


bkr0825
12-30-2008, 07:09 PM
Hello all! Happy holidays!

I have a '97 blazer 4.3l 4dr 4wd with about 150000 mile. I did a lot of work on it over the past year from a new fuel pump, cat, O2 sensors (all4), spyder injection assembly, new plugs, new wires, new distributor, trans flush, new 4wd components, etc...I did not drive it much over the summer (maybe about 500 miles) but I live in Michigan and we've had a good amount of snow lately so Ive used it quit a bit since November.

I cant pinpoint the exact time but I recently noticed when I tried to slow down for traffic lights, etc...that the rpm's stayed up about 1200 to 1500 or so. Sometimes I would come to a red light and stop and the rpms would stay high until I came to a complete stop then they would actually drop back to normal. When I had it in park the rpms would range about 750 to 800. When I put it in drive from park the rpms would drop to about 650 or so.

At speeds between about 35MPH to about 60MPH if I would take my foot of the gas the blazer would barely start slowing down. The rpms would stay up as if someone still had the foot on the gas.

I would pull in my driveway to stop and back into my side drive and when stopping the rpms would stay up and the vehicle would still want to keep driving forward until I put the vehicle in reverse. Once back in park position the rpms would stay up and then after a few seconds would drop back to around 750 to 800. I have a scan tool to read codes and rpm so that is how I know the rpm readings for sure.

I read up on the posts and decided to take out the IAC and clean it. I did that but I came accross a brand new one (AC DELCO) for about 30 bucks. So I replaced it yesterday. I noticed when I first started it up the rpms jumped to about 2000 for a bit before settling back down.

I now not only have the same problem as with the old IAC but now the rpms are even higher and when I slow down for a traffic control device I have to put the vehicle in neutral to get rpms to go back down. I am now getting code PO507 again.

I would really appreciate anyones help / advice with this. I wasnt sure if the problem is with the throttle position sensor? The trans is shifting ok and when the chevy dealer changed the trans filter and fluid last year they said it looked very clean?

Thanks again for any help! Bryan

Blue Bowtie
01-01-2009, 01:33 PM
High idle is caused by excessive idle air. This can be from a sluggish IAC, or from many other sources including: Sticking throttle plate in the throttle body; Sticking or sluggish EGR valve pintle; Power brake booster vacuum leaks; PCV valve sticking; Vacuum hose damage or failure; Loose and leaking joints at the intake, throttle body, or fuel injector lower seals; Sticking EVAP purge valve; Erratic TPS signal; Other causes I'm probably overlooking.
Verify that there are no significant vacuum leaks, check the EGR valve for leakage (random carbon chunks are commonly found in the EGR pintle on these engines), and that the TB is clean and tight.

bkr0825
01-02-2009, 06:09 AM
Thank you Blue Bowtie for taking the time to respond to my problem!

I am in the process of finding the problem and solution. As soon as I find the problem and fix it Ill post what I found!

bkr0825
01-09-2009, 11:50 AM
PROBLEM SOLVED!!!!

Thanks again to Blue Bowtie for you advice.

After poking around the entire top and bottom of the engine and trans for vacuum leaks etc... I decided to start looking at the EGR valve, throttle body, etc. I took the throttle position sensor (TPS) off to test it. I noticed immediately that I could turn the center plastic part of it freely with my hand. I could spin it 360 degrees. I know that it is not suppose to move freely so I suspected right away it was toast. I replaced it with a new A/C TPS and after an entire day of driving my blazer the problem appears to be solved. I had replaced ALL the vacuum lines including the EVAP about 10 months ago so I felt pretty good that it was not a vacuum leak but you never know.

I noticed before I replaced it that when I got up to about 30 MPH or more that if I let off the gas pedal my blazer would actually begin to increase its speed all on its own. Also when I first put the vehicle in drive and held my foot on the brake the rpms would shoot up and stay up and it was like someone was pressing on the gas while I had my foot on the brake.

I just wanted to put that out there to possibly help someone else out that might be experiencing the same problem.

Add your comment to this topic!