mzman

The car is a ‘88 944 Turbo.

I am having an issue where if I quickly let off the gas and allow the rpm’s to drop suddenly the car won’t “catch” it when it reaches idle and it will just stall out. I can stop it by slowly letting the idle drop or let it drop quickly and manually catch it by adding a little throttle around 1200rpm. Oddly it seems worse when I am going up a hill and coming to a stop, not sure why that would be…

I have had this problem for quite a while now, it started right after I added the Lindsey maf and mafterburner piggyback several years ago. Since this isn’t close to my daily driver I haven’t bothered to investigate it further but I am trying to get some bugs worked out of the car now and this is by far the most annoying one.

Right now I’m thinking it has to be tuning related because of the proximity of piggyback install but not sure where to look, the logs seem pretty good. My second guess is ISV, but I’m not 100% sure of all the symptoms of a stuck or failing ISV.

I have been busy working on my other cars and haven’t had much time to work on my pcar recently so I might be out of the loop on these cars so bear with me here.

Bri Bro

First step is to adjust the idle.
http://www.clarks-garage.com/shop-manual/fuel-08.htm
Then look at the idle stabilizer
http://www.clarks-garage.com/shop-manual/fuel-21.htm

User 52121

Well my first guess would be "vacuum leak." Especially if it happened right after installing the MAF - so you were rooting around in there, moving and connecting hoses, etc.

I'm not too familiar with the mafterburner stuff but there might be a setting needed there, too - I'll let somebody else comment.

My advice would be to look through all your hoses and clamps and make sure you have no leaks.

67King

There should be a built in strategy to keep the engine from going into its "friction hook" stage, which is an RPM point so low that it can't be recovered from, and will stall. With the change in the air meter, the base code is probably not compatible. Typically, you can't fix this unless you get into the code and change the strategy, so a piggyback isn't going to cut it. You may be able to get around it by increasing your idle speed, or maybe cleaning out your ISV. Most folks that tried that with Ford 2.3 turbos ended up pulling off the systems until proper MAF conversions came out, but the 944's seem to generally be more tolerant of MAF conversions without the subsequent strategy rewrite (note strategy <> tuning).

mzman

Idle has already been set to ~850.

But I have not checked the ISV as stated in OP. If nothing else works I will dig in there and give it a shot.

I get 22-24 In.Hg vac seemed pretty good to me and didn't think I had a vac leak to be concerned with that reading?

I have lindsey racing 951 Max DME and KLR chips configured for my setup with a MAF. I would of thought that should have corrected code.

I am thinking I will increase the idle speed to 950-1k and see if it helps the issue out.

Bri Bro

The Tach on these cars is not that accurate. Try setting it at 1000 RPM and see if what that does. You do need to install the bypass plug to set the idle correctly.

I ran the MAX chips in the past and had no idle issue so I am guessing the code should support any idle transition.

mzman

When you say bypass plug you are referring to jumping the two pins in the diag plug correct? Its been a long time since I set the idle but when I did I jumped the two pins clarks garage said to use.

You aren't kidding about the tach accuracy it is way off on mine. I use an external tach to set idle, and when the dash reads 750 its actually 850 on my external.

blown 944

Your tps may not be working or set properly.

That's the first thing is check, then the isv function.

mzman

I thought about this. But I thought faulty TPS presented its self in either, fluctuating idle, low boost, misfires, slow accel?

My idle is solid, and I have no other driveability issues... except for the idle stall in this particular scenario obviously. But I will put TPS back on the list and check it out tonight, thanks!

Techno Duck

I also recommend making sure the idle is set correctly first with the ISV disabled.

Another thing, are you running a lightweight flywheel? The same thing happens with my car.. if i am hard on the gas then clutch in at redline to coast the car has stalled on occasion. Only started happening after i installed a lightweight flywheel (9lbs or so).

mzman

I will double check the idle with my external tach tonight with ISV disabled. Thanks

Lightweight flywheel... hmm I will have to check my receipts when I get home. I have lost track which of my cars have one and which don't. The way I remember it is that I just had the stock fly resurfaced when I did the clutch on this one.

67King

The answer given during one of these threads about that was that the transfer function is different. That is tuning the existing strategy. A MAF convesion involves a whole lot more than that, because the strategies are different. An AFM system measures only volume, then infers MAF, whereas a MAF system measures it. Mass = F(volume, pressure , temperature). There is plenty written on this forum about it, do a search. Rogue and Vitesse have both rewritten the underlying strategy in their MAF conversions. Lindsey obviously has a strong reputation, and many people are happy with their systems.

This may or may not be what is going on. Like I said, the 944's are pretty tolerant, unlike some other applications. But working, and working properly are not necessarily the same, and your failure mode sounds like one of the many failure modes I've seen in other applications.

brrgrr

Please continue to update on this thread - I have the EXACT same problem. I have a LR MAF, 951 Max chips. If I am on the gas above 3000 rpm or so and depress the clutch, the engine will stall ~50% of the time. Sometimes it will "bounce" and catch itself just before stalling.

If I coast to a stop sign while still in gear, then depress the clutch, no issues. Idle is fine, right at 900.
AFR's are perfect in every situation.
Warm vacuum is at 20 inhg.

I will double check my TPS and clean the ISV.
I did change turbo's over the winter so I will also double check for vacuum leaks- or maybe I set the throttle cable too tight and I am cracking open the TPS even when off the gas ???
Any help is appreciated.

mzman

Hmm interesting, I must of missed those discussions. I'll do some research on it.

Not trying to start a tuner war here but it seems to
me your suggesting it is an inherit problem with first gen Lindsey racing maf conversions and my best solution would be to switch to a Vitesse or other setup?

I have been seriously have been considering it,just not sure if it would be worth it because I hardly drive the car.

67King

MAF conversions have been misunderstood by 99% of the public for a long time. That allowed some real crap like Pro-M to get out on the market (ever seen the ones with the potentiometers!?). When I say real crap, I mean that when a front came through and the barometric pressure changed, the tune went to crap. Most 2.3Turbo Ford guys I knew that had them ended up taking them off. The 944's are more tolerant than a lot of others. And like I said, Lindsey has a very good reputation, so I am not knocking them, but the issue is really a software/coding issue, and that takes a very different skillset than even the best engine builders and tuners have. I had a friend who wrote strategy for Ford who had a 2.3 Turbo, and he and I did a lot to make a good system for that engine (and he did most of the heavy lifting). It involved a whole lot more than just changing a transfer function, which is what most aftermarket systems do.

But again, like I said, you can probably get around the issue by cleaning up the ISV and increasing the idle speed. The Vitesse and Rogue systems are the best optoins out there, but obviously, there is a big investment with that. If I were in your shoes, I would probably be inclined to try to make what you have work. There is no way I could do what those two guys did.