Hello everyone. I am having a problem with my engine "surging". I just had a brand new AC Delco Idle Air Control Valve put in along with an AC Delco Throttle Position sensor yesterday. The truck is still having the same results, if not even worse. After I got the truck back yesterday, I was driving and I was coming to a stop behind a car at a red light, and I almost hit it, because the engine "surged" and it was harder to stop than usual. I have no Service Engine Soon light, so there are no codes present. Also, after the truck has been completely warmed up, if you park and shut off, and then when you turn it right back on again, the engine turns on "surging" at higher than normal rpms and then gets normal. There are times also after it is completely warm, if you stop and put it in Park, the rpms "surge" up, and then they go back to normal again. I don't know if it could be a bad EGR valve, or something else. If the EGR valve was bad, wouldn't I get an SES light? Any suggestions would be greatly appreciated.

 

Welcome S10Blazer! I'm really new here too .
In my simple mind it sounds as though your PCM is getting an "I'm still cold signal". So I'd be looking at my CTS and see if the connections are up to par while I was waiting for a more knowledgeable member to help out.

 

Actually today, I popped the hood again, and noticed a hissing sound while the engine was running. One of the vacuum hoses that goes to that big black ball was dried and rotted right at the tip where it goes connected to the T-fiitting. We cut off the bad part, and put it back on. I have no more problems as to stopping. But after that I went to the car wash, and had my truck detailed. After I started it up at the car wash, it started up at high rpms, and then it got normal. Then I put it in drive, and it surged a bit. So now the only problem is really at start up. It doesn't stay revved while I'm driving anymore, cause I have taken my foot off the gas at around 30 mph and it loses speed like its supposed to. I am going back to my mechanic on Monday, cause I still hear some hissing, but its hard to tell. It sounds like its coming from the back by the distributor, or by the side where the a/c compressor is.

 

if you touch the vacuum hoses and it leaves a black residue on your hands they need to be replaced..thats probably all your issues..good luck

 

Check for any more leaks and hoses that need to be replaced. I'd also check and see if you have a throttle body thats staying partially open when it should be closed. Its also possible that the throttle body gasket has started to leak. If you have a air intake thats not stock or a throttle body spacer the problem could lie as a result of that.

 

There was a vacuum line that was really bad. It was very dry, and when I touched it, it left that black stuff on my fingers. So it got replaced. But the problem still exists. This is what I noticed. If I start the truck in the morning cold or just after I have let it cool down a bit, it will rev up hight (about 900 rpm) then drop. As soon as I put it in drive, it will rev up up again to about 800-900 and stay like that. It makes it harder to stop, cause you can hear it rev while I'm stepping on the brakes. It stays reved until it gets warm after driving for a while. After a while of driving, it pretty much goes away. I was thinking also as someone mentioned above, the coolant temperature sensor, but I am not sure.

 

The high reving is still probably a vac line, if you have one bad most will be bad also. So much stuff on these is controled by vac that one line can cause a ton of issues.

 

I was actually thinking about that. lol So can we eliminate the possibility that it was the coolant temperature sensor? Also, is there another way to check for vacuum leaks, other than listening and feeling for it (such as any readings)?

 

You may be able to hook up a vac gauge and see what its reading but someone will hopefully have the normal vac pressure. Ive heard of people using a torch that was off to follow the vac lines and if there is a leak you will hear the engine change rpm while you are over the leak.