PCA SDR

OK, I've recently done a full tune-up with plugs & wires, cap & rotor, air & gas filters. It ran like a bat oughta' hell for awhile (well, as much as a 924 can), but now my 924S has developed some hesitation right around 3700-4000 rpm under hard acceleration. Checked timing, it looks fine. Could this just be an old MAF sensor going bad and if so how do you check such a thing. Any other suggestions much appreciated.

Depending on your year, you may want to check the "gate" in the MAF for gunk/sticking issues. The gate is just inside the MAF housing, just inward of the air filter. So:
Remove air filter
With a small mirror check the gate and surrounding area for dust residue, oily grime, etc.
Using a dry towel wrapped around the handle of a docket-wrench or handle of screwdriver gently wipe around the area where the gate travels. Gently open and close the gate ... slowly ... while cleaning/wiping the surface there the gate runs along the walls of the housing.
Be very careful not to scratch, gouge, or maul the inside of the housing or the gate itself.

If the area looks really dirty and gritty, don't touch it yourself, take it to a qualified shop for cleaning. Remember, there's nothing inbound of the MAF to catch/filter any crap that gets dislodged. If you poke grit, grime, or rubber pebbles/smutz into the engine from here you could be in big trouble. Nothing says nightmare like crud in your throttle position sensor, stuck goo in your intake valves, etc.

Another stumbler can be an old ignition wire that's shorting out somewhere on the engine. If your ignition wires are old/faulty, you can get intermittent grounding ... causing stumbling.

There's also the case for a bad ground-wire somewhere. Check all the grounds. Your car is now old (I know about old ... believe me!) and things like ground-wires and their connection points get fatigued (I know about fatigue, too). Give all your grounding points a good review.

Finally, my old 944 2.5L always had a tiny hesitation when going to full throttle from half-throttle. It was, according to several top technicians, part of what makes Bosch Motronic an interesting management system.

Hope that helps. Good luck.

If none of Dan's very good options solve, could also be fuel pressure. I had this same problem on an early 944 and it turned out to be a weak fuel pump (though the in-tank screen can also be clogged).

If the hesitation started after changing wires and cap, you should check the coil wire and cap where the button to rotor contact is. If it was there before, could be a weak coil or one on it's way out.

Wow, how in the hell did anybody fix there own cars before the internet!
So many possible scenarios for one problem. Thanks for the input gentlemen, as I'm sure each and everyone of your suggestions could inevitably fix someone's problem in the future. Quite a list there and it actually turned out to be something entirely different. I came across an identical description in the 944online blog and they had a link to a Yahoo video showing a fix for a worn wiper path inside the MAF sensor that can cause this exact hesitation. For anyone that may have a similar issue, check it out. It's back to feeling it's smooth peppy self again.

http://www.youtube.com/watch?v=-11J8XawQtc

CrashBrown wrote:Wow, how in the hell did anybody fix there own cars before the internet!
So many possible scenarios for one problem. Thanks for the input gentlemen, as I'm sure each and everyone of your suggestions could inevitably fix someone's problem in the future. Quite a list there and it actually turned out to be something entirely different. I came across an identical description in the 944online blog and they had a link to a Yahoo video showing a fix for a worn wiper path inside the MAF sensor that can cause this exact hesitation. For anyone that may have a similar issue, check it out. It's back to feeling it's smooth peppy self again.

http://www.youtube.com/watch?v=-11J8XawQtc

Great. Sounds like you've got it licked.

And ... uhm ... not to toot my own horn too loudly:

"you may want to check the "gate" in the MAF for gunk/sticking issues."

That was #1 on my list.