HELP 3.2 L engine stalls, surges wildly, then OK

[litning]

I dropped an '87 3.2L engine with 54K miles on it, into my '77 Targa about 4 years ago. Best thing I ever did; all of the power and performance you could ask for. However, randomly, about every 5 months or so the engine tries to stall and die, usually after I have been driving for 30+ minutes. I can't tell if it is fuel or ignition, but it hesitates, and tries to quit. After pulling over, it will surge between 500 and 1200 RPM while I try to nurse in just enough gas to keep it running. Then after 6 -10 surges it catches and the RPM blows through 6500 for just a moment, and then back to normal idle. Then it runs just fine for another 3-6 months. The gas tank and fuel are clean and everything else physically looks OK. But WTF! My local shop suggested that the Air Flow Meter (very expensive of course) could be the culprit, or possibly the "brain", the engine control module. Has anyone else out there experienced this problem?

[r-mm]

To eliminate variables, did you replace the various senders/sensors when you dropped the motor in?

BTW that is SUCH a great color - what is it? Kiln Red?

[MMiller]

AFM- not to expensive for a good used one. I picked up one here...looks like he may have another.

Air flow meter 1986 3.2 Carrera [86airflow] - $150.00 : Clewett Engineering, The complete solution for ignition & fuel injection

My 3.2 had similar issue and ended up being a bad connection in the wiring harness between DME and the engine

regards,

[litning]

I'm the original owner (89K miles)! I did repaint the front hood, light rings, and windshield bar due to road grit blasting. I always thought the color was Burgandy Metallic, but that's not in the paint charts. THe ECU was rebuilt 7K miles ago when I swapped the engine. The Head Temp sensor was replaced 3K miles ago. The DME was replaced 1500 miles ago (precautionary change), but the reference sensors have not been changed out. It's scary when the engine just mushes out with a pack of other cars hot on your tail, but that wild surge through 6500 RPM makes me fear for my engines life. Has anyone experienced that wild surge in RPM from stall to full throtle in 1-2 seconds? I'm going to check the wiring harness connection at the ECU and DME next. I would pay most anything for the part that will fix this issue, but I dont want to replace every part until I find the solution, besides the problem is intermittant every couple of months!

[dshepp806]

Does this sense of "surge" feel like something is binding in the throttle path? I'd check that first.

BEST!

Doyle

[VMAX1]

Have you tested the idle microswitch? No expert, but when you unplug, the idle should goes up, per a test. Shouldn't rev up to 6500, though.

[jager911]

Check your throttle linkage under the gas pedal, mine was bent and hung up on the tunnel.
The color appears to be Salmon (metallic), original color on my '74.

[S4hounddog]

Throttle position sensor, it's basically a reostat which could begiving a faulty signal or the next culprit could be the 02 sensor but I suspect if that goes it would be rich or lean - not a surging problem.
My $ .02

[litning]

I appreciate all the inputs. All of the throttle linkage and physically moving parts seem to be doing just what they should. It only happens every 8- 10 drives, abut suddenly it feels like fuel starvation (I cant tell if it could be ignition due to the Motronic brain running everything). It doesn't sputter, or make any sound, it just kind of "mushes" and doesn't respond to the throttle. If I then get it over to the side of the road and try to nurse the RPM to respond to the throttle, it will surge slowly (2-3 second duration) between 500 and 1200 RPM, perhaps 6 - 8 times, and then WHAM, it screams up to 6500 RPM before I can do anything about it, then it comes back down to normal idle. As soon as I can dissapate the adrenaline in my mind and stomach, I realize that it is running perfectly again. Really! I am not depressing the gas pedal very much when I am nursing the RPM; I am just adding a little gas when the RPM begins to fall. It's crazy! - and unrepeatable in the garage or shop.

[Tippy]

Throttle position sensor, it's basically a reostat which could begiving a faulty signal or the next culprit could be the 02 sensor but I suspect if that goes it would be rich or lean - not a surging problem.

My $ .02

They do not have TPS sensors and are not rheostats. What they have is a WOT switch.

[r-mm]

Okay just thinking this thru with some common sense. Could the motor scream to redline without a significant air leak? Like even if every sensor and the DME was on the fritz, how could the motor get enough air to pull hard to redline? Doesn't this mean there more or less has to be some sort of leak and or air metering problem? You positive nothing is physically restraining or making the throttle stick? Cruise control disabled? Next time you pull over you should operate the throttle by hand from the engine bay.

[Maltese Falcon]

Have your tech pull out your distributor and examine the section under the rotor section.
My 3.2 dme engine was acting similar to yours, the culprit was that some small mechanical parts had failed in the distributor. This was on a 150,000 mile engine.Since we don't have any change out parts to speak of in the dizzy (except rotor) you never think of looking in there.

[r-mm]

Sorta off topic but im pretty sure you car is salmon metallic and im also pretty sure its one of the greatest most unique 70s porsche colors... Pictures of the color Salmon Metallic?

[kidrock]

I'm curious if the car has a tendency to surge while warm, cold or both?

BTW, that is a super nice example...great color.

[litning]

I'm going to take it in to see "Dr Porsche" this week with a printout of everyone's thoughts. This surge is intermittant (once about every 4 months - I only drive it once a week) and almost explosive. It always happens after at least 20 minutes of driving, so the engine is up to temperature, and frankly I wouldn't want to be out of the car looking at the engine when it did it again. No cruise control on the engine, no apparent air leak issues (it only happens about every 10 - 12 drives), and no throttle link issues in the cockpit (I'll have to check the engine bay better).
BTW - I looked at the referenced page for Salmon color; that is more Orange than mine. I picked the car up new in fall of 1976, but I cant find the paperwork anymore. I remember being told that it was "Burgandy Metallic" - I don't know if that came from the salesman or the guy at DMV. The number on the door frame is 436-9-3, which I think is a color ID.

[CCM911]

I know this sounds really basic, but have you changed the fuel filter recently?

[litning]

I'll check the records, but I think the filter was changed when the engine was swapped to the 3.2L about 10K miles ago. Thanks, I dont think anything is too basic at this point; it's all too strange, but it hopefully will turn out to be something that's not too weird.

[Quicksilver]

There is nothing in a Motronic 3.2 that will let the engine rev to 6500 RPMs unless the throttle butterfly is open. Period. Unless there is LOTS of air it just can't go there.

So for that part of the description there is only 2 possibilities...
- Your foot pressed the throttle full open.
- The cruise control is kicking the throttle open.

From the description something else is also going on but you need to reduce the "background noise" so you can find the core issue.

[litning]

Well, I had it into the shop for a day. Thought you might all be interested in what I had done. Both reference sensors were missing their outer insulation and the shielding was exposed, and there was some corrosion. The corrosion was removed and new sensors installed. I also had the ignition coil replaced along with the fuel filter. I purchased a good used Air Flow meter online, but am holding off on installing it until we see if the other things solve the problem. It drove great on the way home, but then again, it drove great en route to the shop. So, since the problem was intermittent to begin with, I am just going to have to drive it for several months to see if we have really solved the problem. I'll post again after the first of the year (or before, if the problem reoccurs). Thanks for everyone's inputs!

[pookie]

Thanks for posting what you replaced. Did the shop check the throttle linkage from pedal to engine?

I have a 3.2 in my 76 targa, so I am always curious in those running similar swaps.