Hey Everyone,

The hunting problem that I had thought was fixed has seemed to return. After a couple of days of running without a problem, the problem has returned. At startup it will almost stall out as it tries to find the right idle. Once it finds it, it will hold steady. I can get it up to temp and it will continue to run fine as if it's learned its proper setting.

However, as soon as I turn the car off, let it sit for a minute or two, come back, it will act as if it has forgotten its settings and will start to act up again. After a little bit of driving it will settle itself out and run normally.

The question I'm wondering at this point is, is it the MAF that's causing this or could it be the ECM going bad?

Any thoughts would be appreciated!

Thanks!

Vision

 

What have you done so far? Clean the throttle plate? Check TPS adjustment? Any codes? Any vacuum leaks?

 

Sorry, should've included that before. Was thinking people would remember from my previous post a couple weeks ago.

I've cleaned out the TB, installed new IAC and TPS. Adjusted both IAC and TPS. Replaced cap, rotor, plugs and wires. Have not replaced MAF as of yet.

One other thing I did notice was that around 1300 RPM I was getting a skip as if something were firing late. It lasted for about a mile or so and then didn't do it again.

As to vacuum leaks, from what I've checked so far there is nothing apparent. I don't hear any random hissing sounds and didn't notice any damage to any of the vacuum lines.

 

Maybe take a look at the fuel system....perhaps the fuel line/rail pressure is dropping off (for what ever reason) once the engine is turned off and the remaining air/vapor takes a mile or so to be removed from the system.

 

There isn't much learning capability between ignition cycles.

The blm for idle (cell 0) is stored in SAM cell A, and the blm for cruise (cell for 9 or 10) is stored in SAM cell B and applied to all the other cells upon start-up.

These historic blms are typically limited to 118-150. If you car is normally running outside of this range, then the intial blms will be off from the start and won't be corrected for some time in closed loop.

The other thing that is happening on a re-start is that you're going back into open loop. The fueling will be inherently more erratic since it is influenced by coolant temperature and changes in load that are not present in closed loop fueling.

I think you have a general problem in the open loop fueling which is a function of the MAF calibration, the fuel pressure, the injector size, and any sources of unmetered air, etc.

This error tends to be amplified in open loop due the the load based fueling.

Without scan data to see the MAF flow, blms and IAC behavior, it is difficult to say what could be wrong.

 

Thanks for the feedback guys. I'll see if I can't get a decent scan and some results to bring to the table to try to help pinpoint things a little bit.

On the fuel piece, let's say for the moment that pressure is dropping off and air is entering the system and just takes that time to burn off. Would that make a difference then in how quickly it would start? For instance, one time I can turn the key and it will fire off the first or second crank. Other times it takes a few more cranks and I have to hit the gas a little to get it going.

I think I know what the answer is, but I'm not one of those smart ASE certified guys so I must defer.

Thanks again for the help!

 

I think if you unplug the MAF, and the car runs better that means the MAF is bad.

If you hit it when the car is running and the idle changes I think that indicates it is bad or its on its way out. (correct me if i'm wrong)

 

on the sometimes fires right ou and other times takes a lot of cranking sounds like fuel pump relay or fuel pump,
on the surging, disconnect the electronic spark control over by the heater while it's running and surging. If it smooths out immediately, it could be the ESC, it was on my 86.