Running rough until warm

The code 34 is the MAP Sensor and the code 44 is the O2 sensor reading lean.

How is the lean reading corrected?

It sounds to me as though the MAP sensor is telling the computer to cause less fuel to be injected into the engine. I would replace the MAP sensor first or clean it, and then reset the computer and see if it still throws the code.

we have put a brand new MAP sensor on it already, as well as new O2 sensor and TPI.

Ok. Verify that both are the correct part numbers for your truck. Make sure the connections are good and solid. Make sure the MAP sensor is properly installed. Make sure the wiring between the MAP sensor and the computer and the O2 sensor and the computer is good.

Also, have you reset the computer since replacing these parts?

no,have not reset the computer. after installing all parts,runs rough until warm. I'm reading articles that says that it could be a MAF sensor,but do not know if a 3.1 even has a MAF sensor. I can't get clear information on that,my Chiltons says for 3.8 motor,but other places say differently.

What model Chevy is it?

1994 lumina APV 3.1

Our reference only lists a MAP sensor for your vehicle. We use Mitchell, which compiles information from the manufacturer.

Do a compression test. Check fuel pressure. I would also run some fuel system cleaner through it. Also check for vacuum leaks.

thank you !

You're very welcome. Let us know what happens.

I think I'm losing my mind ! Now it is fluctuating between lean/rich for the O2 sensor ! it keeps going back and forth between the 2 ! what now?

That sounds to me like it's either a wiring or computer problem. Or maybe a faulty O2 sensor. Even new ones sometimes have problems.

hush ur mouth ! :-) I'm so darn upset I don't know where to look/check next. suggestions? P.S. this didn't happen until we ran Sea Foam thru both fuel tank & injectors on top of motor.

until we did that,it only still read lean.

How do you do a compression check? I have a fuel pressure testing gauge available to use but no idea of where hook up for it is located. We have to get this going soon as other vehicle we own has other problems and I'm worried it will go down soon as well. We both depend on it to get to work (different shifts). :-(

Compression is the amount of pressure built up in the cylinders when the piston moves up. To test it you remove a spark plug and crank the engine over. I also like to disconnect the coil to keep the engine from starting. You have to test each spark plug/cylinder. You can borrow a compression tester from places like Autozone and Advanced.

Look for what looks like a tire valve near the throttle body/fuel rail. That's where you check fuel pressure. You should carefully bleed some of the residual pressure off (like throw a towel over the valve first to prevent spray all over) before hooking the gauge up.

codes as follows: 22 1/4 TP volt low reading is .77-.80
24 2/4 VSS no signal
33 MAP sensor high reading is 29 KPA volts.97-.99
45 O2 high volts reading is .07-.99

Were you able to find a compression tester?

no. we can't even get the van out of the yard and the other car scares us enough (tie rod ends,resonator and a code for exhaust problems) that we keep it within a 10 miles radius. the nearest auto zone is 25 miles away.

The fact that this one is throwing codes left and right, and often throws conflicting codes, tells me that there is either a problem with the computer or the wiring. First it's reading high on the O2 sensor, then reading low. And then it throws conflicting MAP codes. The VSS feeds the speedo.

I presume 1/4 and 2/4 mean 1 of 4 and 2 of 4?

as far as we can tell,yes that is what it means. don't suppose you would happen to have a clue as to where in the wiring we should start to look? would rather start there than go get a new computer if it isn't needed,that would most likely be last resort. If it does come to that,I'll be asking how to change the PROM over. Am ordering a compression tester in the morning,hope to have by tues and use asap. time can be an issue,husband works 2nd shift.

Check the connectors at the TP, MAP, O2 sensor, and ECU. See if the wires are loose. Use a multimeter to check the resistance of the wires. Check the wires by hand to feel for cracks. Check the grounds to make sure they're solid and clean.

Thank you,I'll tell my husband when he gets home tonight.

Let us know what he finds out.

I will,thank you.

All grounds cleaned,wires checked,seems to be good as best we can tell. still runs like crap.weather permitting,doing compression checks today. ordered computer last friday,can pick up by Wednesday.

The no signal to vss is suspect to me,the speedometer was/is working. makes me lean towards the computer being faulty.

Yep that what is sounds like, please get back to us with the results so it will help others

Best, Ken

Picking up computer today,can't believe the core charge ! I believe it is located behind the glove box in our van. Can you please give me instructions on how to remove the old one and place the PROM into the new one? I'm terrified of messing things up.

Not problem, disconnect the battery first, then locate the ecm, next disconnect the wiring connectors one at a time, remove the small metal cover and then carefully the prom. Install the prom into the new ecm and reassemble. Then reconnect the battery. Please let me know how it goes.

Best, Ken

Changed out computer today. Still didn't fix the problem ! I don't know what to do next ! ;-(

Have you checked for vacuum leaks? I would check around the throttle body using carb spray. Here is a guide that will help you.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Car repair can be a little frustrating, but hang in there it has to be something causing it and we will find it

Best, Ken

read article,will book mark for husband. can you come to my house please? :-) I'm getting discouraged big time. I think he may have already done something similar to this (with carb cleaner even) ,but not sure he did all the places mentioned there.

I wish I could come through the computer to help you. lol I am wondering if you have an intake valve that is leaking slightly as well that would cause this. I don't have a guide for a leak down test but a compression test might do the trick,, here is a guide for you

https://www.2carpros.com/articles/how-to-test-engine-compression


Best, Ken