mzman

87' 944 N/A I have had it for about a month now, and the whole time it has had a slight hesitating when under acceleration, even under normal acc. I thought it was just fuel injectors so I ran 2 bottles of injector cleaner through it and it has not helped. It also does not have any problem when in neutral, only under load.

I know its a pretty broad thing to diagnosis, but if I could just get some things that I could check out that would be great.

Also one last random thing, my car idles just below 1100rpm. Is that normal? Because just a couple of days ago when I would put the clutch in, to shift and the the revs would drop down to around 850-900ish range but would get a bad rattling and vibration, then it would go back up to 1100ish.

jpk

I'll suggest a couple of sites. Start with frwilk.com He has a really good explaination about how the fuel injection and engine control systems (DME) work. If you have a basic understanding of how the system works, it'll give you an idea of what to look for that would help to narrow things down.

Another great site that you might have seen refrenced in some other threads is clarks-garage.com
Lots of great troubleshooting and repair info there.

Just off the bat - here are a few possibilities:

What's the tach do when it hesitates? if the tach needle dips, it's likely DME relay or ignition realted.
Does this happen at consistent throttle opening - 1/4 throttle, 1/2 throttle etc... - might be a throttle position sensor.
Check any fuel delivery issues also - fuel filter, pump and the pressure regulator and/or damper (including the vacume lines to them) could all lead to a hesitation.
Another possible culprit is the air flow meter.
Other possibilities are engine speed sensor and crank position sensor.

Also - the idle speed dip is nothing to worry about. it's totally normal for this system.

These fuel injection systems are really pretty straight forward. They're also quite reliable and overall pretty trouble free, if you consider that you're dealing with a 19 year old car. Good luck.

FRporscheman

Go get a Haynes repair manual for the 944. It has procedures for testing a whole bunch of sensors and stuff. You should get all the sensors (TPS, AFM, temp, oxygen, etc.) checked. Also, you could have a broken fuel pump check valve or a clogged fuel filter. I'm not sure of the symptoms of failure of either of these parts specifically, but you might find something if you do a search.

Start with the O2 sensor.