Have a question guys. Does it sound like bad TPS sensor. Car has been idling high, around 1500 rpm range. I take my foot of the accelerator and the car just keeps going! The issue I’m having is, besides that. It also goes back to normal rpm range around 5-600 rpm while idling. My high throttle is intermittent if that makes sense. On the 91 Camaro you can’t adjust the TPS. It just screws in and is set.

 

That sounds more like a leaking or binding throttle body. If the bores, plates, and shaft have not been thoroughly cleaned in a while, it might be time. Even if that is not the problem, cleaning will eliminate that as a question.

 

You are correct that the later ECM sees the TPS location, sets as zero, and works from there. Mainly on Delta TPS%.

It is easy to test, probe it, check the voltage, slowly open the throttle and observe voltage change. Should be smooth. If not, bad TPS. The TPS is used for determining Accelerator Enrichment, Power Enrichment, and a few other things with fueling and spark advance, but it shouldn't hang the RPMs up as it doesn't actually allow more air into the engine.

While checking the sensor function itself, as Vader said, check the TB. Make sure it closes smoothly and you may need to inspect for vac leaks in the area. I also support a good cleaning for a "just to be sure".

 

If it was a vacuum leak, wouldn’t it idle high all the time? So pretty much before all this, I just replaced my fuel injectors, fuel pressure regulator, all the runner and plenum gaskets, cleaned everything completely, no carbon buildup, bad IAC maybe? I replaced that 3 years ago. Car runs great now, besides this high idle. And like I said one moment it will idle awesome, than out of the blue idle high. Throttle bodies don’t need to be lubed up or anything right?

 

Depends on what is creating the vacuum leak.

Bad IAC maybe because it is slow to respond or over traveling? Data logging would help.

Sounds like a ridge may be preventing the blades coming back fully closed.

It's hard to fully diagnose an issue remotely, we are just giving you suggestions on troubleshooting based off prior experience. I would think if you had a bad IAC you would be bogging or stalling due to lack of air as the IAC tries to take over. However, I wouldn't say you could fully eliminate it, I would just start with the TB. Leaking shaft seals, ridges forming, and build up have all been known to cause high idle. Doesn't mean we can be 100% sure that is your problem, but it has occurred enough that I think you should start there and eliminate it. Just as I think you should test your TPS and eliminate it being the issue. While you are there you will get a feel for the throttle movement.

 

Yeah I know it’s pretty difficult to diagnose remotely without actually seeing it. I appreciate all the help I get from you guys. I have a question, you know how the bottom of the throttle body comes out? The part where the coolant line connects. I forgot to clean that out. Would that affect the idle at all?

 

I wouldn't think so, the coolant isn't supposed to mix with the air. It could crack and leak I guess, but I have never heard of the coolant leaking into the motor through the TB. Anything is possible with enough time and miles though.

I would focus on verifying the TPS works correctly, the throttle blades move correctly, and the TB is clean before worrying about other items. Once you have eliminated the common issues, then move to the "what if's".

 

Yeah I cleaned everything really nice, used Degreaser and cleaned it in all in the basement sink haha.

 

We have a big parts cleaner at work I love having access to.

Did you check the internal bores for any ridges?

 

I’ll look right now and check it out.

 

So I think I found out the issue, I have a leak in the lower intake manifold! I can see like air pockets escaping.

 

I tried sending a little clip but it didn’t work lol

 

YouTube and post link.

what part of the manifold?

Hard to make sense of a crack being intermittent. I am curious. We might all learn something.

 

 

So it’s right by the bottom of the runners on the firewall, driver side. Think I can patch it up with some sort of sealant? Haha
I’m also wondering if I caused it to leak or if it was loose already. Because I had to really pull on the fuel rail to get it out of the manifold.

 

My 89 350tpi Iroc does the same thing...does it when starting and in neutral and park...

 

The high idle? I mean it sucks, because there’s a whole list of items to check off.