Topic: 99RS starts fine then stalls. Solved

[flyboynextdoor]

Hey Guys,
I'm pretty new on here but had my RS for a little while.
Got my self a real mystery. Driving out to work my car just died like someone turned off a switch. Its home in my garage now.

It will start....then it dies.
It will run for maybe 5 seconds then sputter and die.
If I try to start it right away it will run for maybe 2 seconds.
If I wait a long while it will run for a little longer 5 seconds or so then die.
Giving it gas after starting doesnt help.
No codes

My first guess was fuel pump or regulator, replaced both those.
Also replaced the fuel filter.  I've got a new MAF on order but I'm not sure that will fix it.
No luck its still the same condition.
I have cleaned the MAF and checked the cam and crank sensors. Nothing has helped.
Theres a couple guys on rs25.com that are also having the same issue right now. Were all stumped.
Anyone seen this before or offer any suggestions?

I dont want to bring it in just so the mechanic can scratch his head too.
EDIT
(After swapping out most of the major fuel system components nothing worked so on a hunch I put in a new MAF and it ran great immediately)

[seat safety switch]

Have you tried unplugging the MAF and see if it idles?

[RJK]

i had the same problem, pulled the throttle body out and cleaned it and now it runs like a dream. is an easy place to star and could be a 5 dollar fix..

[flyboynextdoor]

Yeah I've tried unplugging the MAF. didnt help. I've got a new one coming anyway. I never thought it could be a dirty TB. Specially since it just died like someone turned off a switch. But I'll try cleaning it and see what happens. maybe do some polishing while I'm in there 

[flyboynextdoor]

I checked my plugs, And they are gross. I cleaned and re-installed them but no different, not even a little. It still stalls after just a few seconds. They were black with carbon but I'm not sure if this is a symptom of the car not running long enough to burn this stuff off or if its a symptom of what made the car break down..... The car will always start.... I recently changed them (spring time) and the old ones were cooked but not BLACK! plus I had them out to check compression not long ago and they looked good. I also found number 3 plug wire is really loose at the coil. I'll see if there are any replacements in town tomorrow. I dont believe the coil is my problem since the car shouldnt start at all if it were, but that #3 wire isnt helping. Cant imagine what my TB could have to do with it unless its the TPS or that other electrical deal at the top. I'm gonna look through my manual tonight and call the nearest suby dealer in the morning. Looong ways away.

[Guglianoh]

Timing belt jump? Try unplugging the crank sensor and see how it runs, if it does not stall ur belt could have jumped

[flyboynextdoor]

I thought about that too. I might pull the timing belt cover and see what I find. The marks to set it properly should still be there.  Thats a lot of work I'm hoping to avoid though. I just did the timing belt last year and car has run like a top till now. I have pulled the cam and the crank sensor and both times the engine wouldnt even fire.
Anyone know what the second harness is for at the top of the Throttle body? I know the one on the right side of the TB is the TPS.

[Guglianoh]

Only pull the crank sensor the engine uses the cam sensor to start, if u pull the crank sensor it should run. If they are both connected and it senses that they are out of sync (timing belt jumped) it will cut power and the engine will die.

[smrt_ass_engr]

Im starting to think it could be the battery or electrically related anyways. 

Clean and check your grounds lately? 

[flyboynextdoor]

Only pull the crank sensor the engine uses the cam sensor to start, if u pull the crank sensor it should run. If they are both connected and it senses that they are out of sync (timing belt jumped) it will cut power and the engine will die.

That sounds like a pretty informed appraisal! Is that how it really works or is that a very descriptive guess? One of the guys on rs25 had to bring his car in and it sounds like the dealership is searching for a needle in the haystack. I guess I'll be pulling my timing covers off!

[flyboynextdoor]

Are timing belt slips that common??? This is my first vehicle with  timing belt. I'm gonna assume if it did slip it was at the crank cog. Kinda ittshay setup if they slip that easy how does anyone turn the power up and drive these cars hard??

[AWDFTW]

Nobody does on RS' haha ... And it's not that common but it happens.

[flyboynextdoor]

I cleaned the throttle body and just checked the timing, It looks good, so I'm back to looking for that needle.

[flyboynextdoor]

Even though the car wasnt showing a CEL or any codes I ordered a new MAF sensor just cause it was a cheap item to eliminate on the list of possible causes. The problem with the engine is fixed thanks to the new MAF. What I cant figure out is why the engine would run longer after sitting for a long time but it would barely run for two seconds if I had just attempted to start it. Doesnt make sense to me, oh well. My car is fixed! Just thought I'd post the solution to my problem, thanks for all the advise guys

Now I can overhaul the engine.

[GrantC]

"MAF sensor" includes the IAT sensor.

So hot air + skewed/wrong MAF results = stall?


Ooh, I have a better guess. Maybe the cold start enrichment made it run when started cold even though the MAF was giving wrong info?


Or a mix of both?

[seat safety switch]

Car shouldn't be listening to the MAF at all when it's idling, it should be in straight up open loop and working strictly off the IACV (which bypasses the MAF, doesn't it?) Duh, of course the IACV is post-MAF.

That said, my 97 had some freaky issues trying to idle warm that were corrected with a replacement used MAF (and started great if gassy cold), and I remember on the Audi 5000 that its warm start issues were partially because it was trying to use the damaged front O₂ to attempt "more closed" loop operation instead of its cold start behaviour. My guess therefore is that the ECU just lets it do whatever on cold start (GAS GAS GAS) and then on warm start tries to be more subtle by involving a few of the sensors which eventually involves the MAF and the ECU makes some bad decisions leading to the car stalling.

I'm curious how a more modern Subaru would deal with the problem, considering cold start is a big part of Euro emissions standards now.