The car always starts perfect cold. After the engine is nice and hot and I turn it off, I'd say every 3 out of 10 times when I fire it after 15 minutes of sitting, it will fire and die. Or it will fire and idle at 350-400rpm, and a soon as you tap the gas it dies. The car never throws a code.

Now here's the thing, if I pop the hood and let the hot air out, it will fire and run great after 10 minutes. If I keep the hood closed (trapping the heat in), it might take anywhere from 30-45 minutes for it to fire and idle ok. So it's heat related.

I've replaced both MAF relays and still had the same problem. Today it happened again, so I unplugged the MAF, and BAM it idled perfect! Plugged it back in, and the same thing, it either died, or idled at 350-400rpm. Opened the hood, let the hot air out, after 10 minutes it started and idled fine.

So should I replace the MAF?

 

Hey, did I stump the crowd?

 

You can replace the MAF if you want, but that's an expensive guess. Simulate the conditions, connect a voltmeter to the MAF output, then attempt to start it. That will mean that you'll have to provide leads outside the engine compartment so the hood can remain closed to "bake" the MAF. You could also scan the ECM on startup to monitor MAF output, but scanned data only shows what the ECM is seeing, which is not always what the sensor is reporting.

The one benefit of scanning is that you can also monitor the injector PW, target RPM, MAT, CTS, TPS, and actual RPM.

 

Vader, I did datalog when this was happening. But right now I'm stuck at work on this sunny warm day I'll post it up when I get home.

Thanks

 

I was having mafs problems and just for its and giggles I grabed the terminal and wiggled it around in the connector housing

bam it started to run like it should, letting me know that I had to make each of the five connections a little tighter

I had a code 33 and I wish the helms manual gave little tips like that instead of all the wiriing diagrams and 12v jumpers

 

When I have the problem (The DTC is a stored code because I just set the timing):




Normal idle:

 

5g/S cranking seems pretty normal, IAC is open adequately, ans the injector PW seems long enough to start a warm engine. I'm wondering about the advance at 20º, but it shouldn't be high enough to cause problems.

 

i have a question.. not that i can contribute anything here but was wondering what the AFGs gm/sec stands for?

 

That would be controlled by the ECM correct? To my knowledge, it is stock. Is it not suppose to be that high?


So I take it my next option is to connect a voltmeter to the MAF output?

 

I'm not certain that it isn't supposed to be that high at cranking. I never monitored timing at cranking. At no-load idle, advance may be up to 23º, or possibly higher in some programs.

The MAF seems to be reporting about what would be correct intake air duning cranking at 375 RPM. You can test the output with a voltmeter right at the MAF, but your scan already shows what should be reasonable. If the signal is falling off or intermittent after starting, that's a different problem.

 

I had a similar intermittent problem and it was a bad MAF.

I data logged it and the MAF would never get over 18 g/s of airflow. Idle was fine but any throttle would make the thing real lean. had to limp it back home a couple times.

I put my old maf in (the bad one was a new wells replacement) and it works fine now.

datalogging is the key.

 

Vader, I'm not sure if I am understanding you correctly when you say "cranking". But that datalog I posted where it shows 371 rpm, is when it is idling, not cranking. It will actually idle that low and not throw a code, then as soon as I tap the gas, it will just shut off. Or it will fire up, then just die. Until I let all of the heat out of the engine bay.


Other than this, the car runs/performs great. I can drive it for an hour and a half straight with it at operating temperature and it runs perfect. It is just this random no start/very low idle condition on hot starts.

 

Yeah - Im going to go ahead and say you need a new MAF. At least borrow one from someone for awhile and see if its better.

Best thing you could do is give a data log of MAF flow vs rpm and MAF vs TPS for when you hit the gas and it dies.

This is how I diagnosed mine. I just sat there and watched MAF g/s while it was running and just ever so slightly cracked the throttle. the g's would go up until 18 and then just flatline. if I pushed the throttle any more the engine rpms would go DOWN with the MAF just sitting there saying 18.

I suspect yours has a similar problem but the flatline occurs at a much lower airflow -- Unfortunately your graphs dont show MAF g/s.

BTW mine did this only occasionally but eventually it got so that it was every other time I would start the car.

 

Wow. I cannot find anywhere to buy a new MAF if I did need one. Wells stopped making them. I don't want an adjustable MAF, and TPIParts wants $400 + for a OEM new one. Damn...

 

An idle that low is a problem. Does a separate tachometer (not the instrument panel thing) agree with the idle RPM?

How is the minimum air? If the IAC is providing all the idle air, the IAC steps on hot restart may not be adequate to allow proper idle.

 

I do not have a seperate tac to verify The idle rpm the latop shows matches the idle rpm on my Tac in the car when it's idling that low. I believe it is idling that low, because when it does, it is VERY close to just stalling.

The minimum air is that screw on the throttle body correct? That has not been touched. There is still a cap "thing" on it where you can't adjust it.


Thanks for the replies guys, I really appreciate it. It does this I'd say maybe 3 out of 10 hot starts. If it was the minimum air, would it be this random?

 

No, As a matter of fact you should be able to lock out the Idle Air control motor from the equation by doing the following:

start with the car off but warmed up,
jumper pins A and B of the ALDL connector.
Turn key to on but DO NOT START.
You should hear the IAC motor buzzing or clicking -- this is normal and is the motor trying to close all the way.

Let the little motor close for 10 seconds or so then turn the key back to off.
Pull the jumper out of the pins in the ALDL connector.
go under the hood and pull the connector to the IAC motor (square 4 pin plug)
Now when you start the car the IAC will be closed and will stay that way. If the car will not start when you do this you might start looking at the IAC motor or minimum idle air set screw that you say is still capped on your throttle body.