Unplugging MAS kills motor immediately

[Rock2610d]

Ok so i must be a poor searcher. Looked for an hour but all I got was unplugging MAS made idle better?

When I unplug my MAS my car dies immediately. I did it 3 times. Started car and runs. Unplug MAS and it dies fast, does not even try to keep running, just dies.

If I give it gas it will try to run but misses badly. That is what I expected it to do at idle with MAS unplugged.

Is this normal?

No codes were thrown when I unplugged MAS or MDP sensors.

Please note I think this may be one of several issues I have. I want to diagnose each issue on its own as trying to diagnose multiple issues could get confusing.

This post is one issue.
Engine sounds like a VW bug is second issue and I have a post on that.
Lights dim at idle is third issue.
P0300 multiple misfire is 4th issue.

 

[LandSpeed-DSM]

Well, lets work backwards a bit here to see if we can help you. To your understanding - What does "MAS" stand for? What does it do?

 

[Rock2610d]

Sorry if my terminology is bad. MAS = mass air sensor?

It measures the amount of air coming into motor. It's located between air filter and turbo inlet.

 

[greydelta38]

Ok so i must be a poor searcher. Looked for an hour but all I got was unplugging MAS made idle better?

When I unplug my MAS my car dies immediately. I did it 3 times. Started car and runs. Unplug MAS and it dies fast, does not even try to keep running, just dies.

If I give it gas it will try to run but misses badly. That is what I expected it to do at idle with MAS unplugged.

Is this normal?

No codes were thrown when I unplugged MAS or MDP sensors.

Please note I think this may be one of several issues I have. I want to diagnose each issue on its own as trying to diagnose multiple issues could get confusing.

This post is one issue.
Engine sounds like a VW bug is second issue and I have a post on that.
Lights dim at idle is third issue.
P0300 multiple misfire is 4th issue.

Is it normal for the car to die when disconnecting the mass airflow sensor? Yes. The ECU can't read the air flow and give the engine enough air to combust the fuel and run properly. Every car will do that.

 

[TSiAWD666]

He was asking to make the OP think a bit, not because he didn't know the acronym.

 

[Rock2610d]

If that is normal great, but I thought the ECU would go onto limp mode when disconnecting MAS? And a CEL thrown?

 

[greydelta38]

He was asking to make the OP think a bit, not because he didn't know the acronym.

Whoops- I didn't think hard enough on that post. Gotcha

 

[Rock2610d]

I am sorry if I have posted a poor question, but I vaguely remember disconnecting MAS right after I installed the rebuilt motor and it did not die when I disconnected it. It just idled really bad.

Am I mistaken?

 

[LandSpeed-DSM]

Sorry if my terminology is bad. MAS = mass air sensor?

It measures the amount of air coming into motor. It's located between air filter and turbo inlet.

Right. MAS/MAF sensors (Both are correct, whether its MAS or MAF depends on manufacturer) measure the amount of inbound air so the ECU can calculate the amount of fuel to shoot at it and continue to run, during closed loop operation.

 

[Rock2610d]

Ok, so in closed loop the engine will die immediately if MAS is unplugged and mine is functioning correctly.

Thank you!

**********
UPDATE

After searching for MAF and limp mode, I read several posts that state unplugging MAF sends ecu into limp mode.

So, should it die immediately or try to run? Am I over thinking this?

 

[boost97gst]

It should go in to limp mode and run REALLY REALLY bad. Depending on where your biss is set, it could sputter out and die. If you tune for a high idle like 1k, it may be able to rebound quick enough to stay running, albeit poorly

Whats jumpin out at me is the fact that when you disconnect the mas you have no CELs. There should be,iirc, atleast 2 codes thrown. One for intake temp, and one for something else. Atleast thats what mine does.

Unlpugging mas is only good for maybe troubleshooting and if your stuck somewhere and completely blew a coupler off with no tools at all and no way to get the IC coupler back on.Then you can unplug it and atleast get somewhere. Better than a tow if youre close to home

 

[Rock2610d]

Ok, now that is what I thought too. I am troubleshooting, and since it dies like shutting off the key when I pull the MAF plug I could have an issue.

My Biss has never been touched since the day I bought it off the show room floor back in 1996.

Idle is 740 to 780 rpm hot with a/c off.

Sounds like a BLT is in the future. But that does not explain why I am not getting any CELs. Maybe it's dying too fast for ECU to trip a code?

 

[cyhm]

You are obd1 correct? It generally takes A LOT to throw a code with obd1. On top of that, the codes reset when the car is shut off. Therefore, it won't throw a code before the car shuts off when you unplug the mas (which is normal as stated earlier.) However, if you start the car with it unplugged, it should run poorly and THEN you may get a code. If the car runs fine with the mas plugged in, why are you questioning it running poorly unplugged? Under certain conditions, the ecu may "guess" the correct parameters and continue to run, but yes, it is normal for a car to stall when you unplug the mas.

Edit: I apologize for poor info. Never had a 2g and didn't realize 95 turbo 2gs were obd2. However, it may have a pending code that is simply not thrown active because it isn't cycled enough times before the car dies. Try starting the car up and running it with the mas unplugged and then you will more than likely see a code.

 

[boost97gst]

Yea, it could be shutting off so fast theres no time. Try starting the car with the maf unplugged and see if you can get a code up.

 

[cyhm]

Normally, codes require the ecu to see x number of faults in x amount of time, so you probably have a pending code since the car dies, which won't throw a CEL.

 

[Rock2610d]

Ok, unplugged the MAF and started it. Was able to keep it running and when I let off the throttle it almost died but did not. Had to keep it running like that for 2 minutes to get a CEL.

Here they are:
P0100 Mass or Volume Air Flow Circuit
P0110 Intake Air Temp Sensor 1 Circuit
P0105 Manifold Absolute Pressure/BARO circuit


Do these make sense if MAF unplugged?

 

[boost97gst]

That sounds like your maf is communicating with the ecu properly. Those codes look familiar.
Looks like your maf is at least reporting back SOME info, now the accuracy of that info can only be assessed through dsmlink. You need to log maf values and intake temps to see if something is wrong.

I had to re read your original post. Have you checked idle voltage at the battery? All grounds good chercked?. From your symptoms i think you can rule out the maf. Start looking elsewhere. Cas,cps, ptu, coils

 

[Rock2610d]

^^^^Agreed, I think MAF is good too. Moving on to a boost leak test and compression test.

Thanks

 

[papastalon]

Sounds like you have a misfire. 3 different sources for a misfire condition. Fuel, spark, and mechanical.
If you can get the engine at idle I would start by isolating cylinders. While idling pull one a time a spark plug wire at the valve cover location. If idle changes(RPM drops) then that cylinder very likely is NOT at fault for a Mech./Ignition misfire. If you pull a wire off and idle remains the same you definetly have a misfiring cylinder. I also check for a arc or listen for it arcing when I pull the wire off to indicate the coil is firing. If all test good so far listen for the injectors clicking(hear up to a screw driver). If not and found a misfiring cylinder next would be a compression test. +1 on a BLT and compression test. If idle is going below 750RPMs like down to 500RPMs the Alternator can not abtain sufficient voltage.