EGR valve

[jcoogs]

My 2001 Alero wouldn't start. You could get the engine going by stepping on the gas as you turned the key, but once you removed your foot from the gas, the engine shut off. My friend actually "fixed" the problem for a week by hitting the EGR valve with a wrench as I revved the engine. His theory was that there was a carbon buildup in there and his hitting it had loosened things up. But now the same problem is back. I can't start it up without stepping on the gas, and the engine dies if I let my foot off the gas. What do I do?

[Chris2000]

Originally Posted by jcoogs

My 2001 Alero wouldn't start. You could get the engine going by stepping on the gas as you turned the key, but once you removed your foot from the gas, the engine shut off. My friend actually "fixed" the problem for a week by hitting the EGR valve with a wrench as I revved the engine. His theory was that there was a carbon buildup in there and his hitting it had loosened things up. But now the same problem is back. I can't start it up without stepping on the gas, and the engine dies if I let my foot off the gas. What do I do?

Take out the IAC Valve and clean it off and clean inside of it. Unplug the connector and then there is two little * screws to get out. I cleaned mine out with some q-tips and a rag, but you can use some carb. cleaner if you have it.
The Iac valve is right there when you open the hood it's on or very close to the Throttle body.

It looks like this:

http://www.autozone.com/autozone/catalog/parts/partsProduct.jsp?itemIdentifier=124257_0_0_&skuDes cription=Duralast+/+Idle+Air+Control+Valve&brandName=Duralast&display Name=Idle+Air+Control+Valve&categoryNValue=1599999 9&sortType=&store=2597&isSearchByPartNumber=false& fromWhere=&fromString=search&counter=1&itemId=207-0&navValue=15900207&filterByKeyWord=iac+valve&prod uctId=124257&searchText=iac+valve&categoryDisplayN ame=Engine+Management&parentId=59-0

[clutch1]

First!!!!

Carbon buildup in the EGR system WONT WONT WONT cause a driveability problem.. well, assuming you mean carbon buildup as in a clog.
A clogged EGR will only throw a code/ cause high NOx emissions.

To understand how this works, know how the EGR works. When you cruise the EGR lets in exhaust gasses, which ARENT burnable. These gasses replace oxygen, which in effect richens the mixture. This causes lower combustion chamber temps, which lowers your NOx emissions. EGR only opens at low load cruise situations... if it's stuck open at idle all that exhaust gas will flow in and the car won't get enough oxygen to run.

Next, the reason it worked when he hit the wrench is because it was stuck open, and when he hit it it freed up so it could close again.. and then probably worked for a little while before it got jammed again.
GM's had LOOOOOOADS of trouble with this EGR design... it's crap.
You can look up the wiring diagram, backprobe the position sensor signal wire (I think middle one on the 5wire harness)... should see .5V at idle, and rev it and see it go up at some point when the EGR opens.
Chances are you'll see like 2.5V or something.. that's be around half open. If it's much over .6 - .7 it's stuck too far.

If you don't like testing electronics do this... take off the EGR, plug the hole that goes to the intake, and start the car up. Does it run now? If it does the EGR is your problem.

If it indeed is stuck.. take it off... you can TRY cleaning it... but would probably be best to just replace it.

[jcoogs]

This is all very helpful. Thank you all. However, I went outside today and the car started. This time the Service Engine Light was on. I drove to the Auto Zone and had them read the code. It said that the Mass Air Sensor was bad! I'm very confused.

[clutch1]

Well, OBD2 has 8 monitors, and they run in a certain order and at certain times during a regular drive. If your MAF decided to have an issue, the OBD2 tests will throw that code and stop there, even if more components are bad (like your EGR).

That being said, the tests are usually accurate (except PCV), and if it has an issue it tends to lead to that part. However, the sensors test (comprehensive) can be fooled if other sensors on a circuit are causing issues so forth. IIRC the AC level switch is one of these that shorts out on GMS a lot, but can throw man other codes.

SO! Before you go replacing an expensive MAF, test it!!!
First, simply unplug it with the car running... it should start running like crap or even die. If nothing happens, then the MAF/wiring/harness is for sure bad. If it indeed stumbles/dies/something the MAF is in general working order.

These MAFs are 3 wire I'm pretty sure. Use your multimeter (it's gotta be a pretty expensive one that has an option to read DC Hertz). One wire should have 12v on it. The other should have .0X volts (ground), and the last one left is signal. Once power and ground are OK, backprobe the signal wire and set the MM to read DC Hz. Run the car. At idle you should see 2000Hz. Now, rev it... number should go up. You may need to press something like a max/min button, which will save the max/min numbers and allow you to scroll through. Get it to look for max, now snap the throttle WOT quick. The max it should see is around 8-9000 Hz. If it sees all that, the MAF is good. If it reads, but too low, it's almost assuredly dirty. Pull it out, spray it down with MAF cleaner.

See if that alleviates the MAF code issue. If not you're going to have to start poking around for other things that would throw a false MAF code. The OBD2 tests also test for rationality.. generally MAF will be compared against MAP and TPS. You could test those, too, if you're bored and desperate lol.

TPS signal wire: .5 closed... 4.5 open.. look for evenly rising numbers
MAP signal wire: 1.2 - 1.6V at idle... snap it and look for 3.5v or higher. Also pull vacuum on it and make sure it doesn't leak down.