Infrequent stumble getting more frequent - WTF ??

[docachna]

My '95 944 (126K) started showing a stumble every 15 min. or so, at highway speeds. By "stumble", it felt like a complete loss of power, but only about 0.1 of a second or so --- very brief, but it felt like a "harder" stumble than just one cylinder misfiring. Compare it to completely pinching off a small water hose - just long enough to stop the water -- then immediately letting go and opening it back up again, running at full bore. It's that brief. But, at highway speeds, it's hard enough that you feel it in your seat.

It has now started getting more frequent. Today at highway speeds I was getting one about every 2 minutes, then up to about every 30 seconds. It's never more than one at a time.

I hardly know where to start -- fuel filter, plugs, ignition wires, coil, bad ground somewhere --- just thinking about it is very daunting. I could replace half the car and not come across the real problem.

Any thoughts or suggestions, or somebody that's "been there/done that" ??? I hate to take it to a shop, and have them start "replacing" until they stumble across the problem ("even a blind squirrel finds an acorn once in a while")!!!!!!!!!!!!!! Might a scope at least narrow down the field ?

[billofdurham]

Check engine light on?

Test for fault codes with the On-Board Diagnostic unit in the engine compartment and let us know if any are stored. We can then go on to other things.

Bill.

[docachna]

Check engine light on?

Test for fault codes with the On-Board Diagnostic unit in the engine compartment and let us know if any are stored. We can then go on to other things.

Bill.

No check engine light..........

(Is that a woodie wagon on your signature, or a police wagon ???? My old eyes can't tell the difference anymore.....

[billofdurham]

In our terminology it's a police estate.

Although no CEL it may pay to check for codes.

Apart from that it is a case of rounding up the usual suspects and seeing what develops.

As you have said, fuel filter; plugs; ignition leads; coil; bad earth (ground) plus distributor cap/rotor (if applicable); air cleaner/air intake; uneven compression; airflow sensor; throttle switch and connectors; fuel pressure.

They aren't in any particular order but I would start with the easiest and check the battery leads for tightness and good connections. Ensure that the negative lead is sitting on a good, clean part of the frame and also the earth strap from the engine to the frame is good. Then check every visible electrical connection on the engine for tightness and cleanliness. Pull the connectors off, look inside and clean if necessary.

Bill.