91 Camaro, V6, 3.1 L, Auto:

I started out with a stumbling idle. It was throwing codes 14, 22, and 53.

From what I've read, that's:
14 = Hi Temp @Engine Coolant Sensor
22 = Low Voltage at TPS
53 = Hi Volt @ EGR or Anti-Theft

I replaced the IAC and TPS and then started going thru the "idle learning" process. (and cleared the codes)

After a couple minutes, the idle shot up to about 2500 and wouldn't come back down.

I shut it down and re-checked the codes and now it's showing code 33.

this should be "Hi Voltage @ Mass Airflow or MAP"??

I swapped the air box back to the original (I'd previously swapped in a dual-snorkel unit from my Z28 and thought that it's airflow sensor may not be compatible - although it's been in the car and fine for 6 months).

No change...still idleing way high and still getting a code 33.

It did idle normally, although rough, for a couple minutes - I'm assuming until it warmed up.

I also attempted cleaning the throttle body and I noticed that it's idleing >2500, but the butterfly is completely closed. So, where's it getting enough air to run that high?

Could this be an EGR problem? Should I swap that?

EGRs pretty expensive, so I'd like to be sure. Would just blocking it off tell me anything? How would I go about doing that?

I'd sure appreciate any advice...I'm pretty sure that some sensor or sensors is throwing the ECU off, but it's a major pain to figure this stuff out...

 

Here's an update...

I went ahead and swapped out the EGR with a new one...the old one was looking rusted, so I figured it might be time anyway...

This helped: prior to this, it would idle up to 2500 and stay there.

Now, it starts up and idles ok - although rougher than I'd like.

When driving, and I get it up above 2,000 or so, and then lift (or shift into neutral t really test it), it'll stay idling high (~2000) for about 20-30 seconds before it finally kicks down to normal.

It definately feels rough.

It's still throwing code 33 after a bit of driving.

I tested the vacuum to the MAP sensor and it seems ok - it's the same at the sensor as it is coming out of the back of the manifold (~6-8 inches of mercury...is that about normal - my gauge isn't calibrated well on the low end..)

Could it just be a bat MAP sensor?

I guess that's my next swap and pray...

 

How much vacuum should I expect the 3.1 to generate at idle (in park)?

At this point, I've replaced the IAC, TPS, EGR, and MAP (any other letters to replace?? )

Although it's a bit better, I'm still experiencing the following:

In park, the car seems to idle ok, although a bit rough, but revs up and returns to idle ok - even after it's warmed up.

However, when I drive it, and lift off the gas, the car wants to keep the throttle up around 1500...if I shift into neutral, it'll rev up to 2500 with no load on it. It'll stay there for 10-15 seconds before it finally idles down.
If I leave it in gear, it'll figure out that it needs to idle down a little quicker - maybe 5 seconds.

But, you've got to ride the brake while waiting for it to back off, and it's obviously not real driveable or safe.

And, I'm still throwing the code 33.

Since I've replaced the MAP, I'm now assuming that it's simply too low a vacuum at idle - from what I've read, that's making the ECM think it has a load on the engine, so it's giving more throttle to compensate.

I've checked the vacuum hoses and I can't hear or find any obvious leaks. I've tried spraying carb cleaner on hoses and connections, but I'm not seeing any change in idle when I do this.

I put a vacuum gauge on the port that goes directly to the MAP and I'm seeing about 6-8" of vacuum. Is this too low (idle, park)??

If so, and if it's not an obvious leak, is there anything else that could cause low vacuum?? Anything internal??

I guess I start replacing vacuum lines...maybe blocking off unessential vacuum ports to see if I find any change?

I'm out of ideas and about to give up...I'd sure appreciate any advice...

 

Minor update:
I was wrong about the vacuum level I'm seeing.
More like 10" out of the port going to the MAP.
(at idle, in park...cold engine).

Is that in normal range?

I only see 2 other vacuum ports actually exiting the engine:
One feeds the brake booster and has a T going a couple other places.
One coming off the back of the throttle body...has a rubber connection there that feeds lines to a vacuum servo under the plenum (for fuel injection?) and another goes off to the charcoal canister (I think that's what's next to the air filter box behind the passenger headlight).

If I block either of these, I'm not seeing any increase in vacuum, so I think that tells me that there's no leak in any of those vacuum circuits...

so, I don't really think I have any vacuum leaks...yet I'm still getting a low vacuum error code (33) and I have a brand new MAP sensor...