Porschenut_Lee

For the record, I did a search and have some ideas. None of the threads I read showed both of these issues simultaneously. It was one or the other. I'm hoping someone else may have experienced both and can point me in the right direction sooner.

Background:

Just purchased 1990 C2 Coupe 73,000 miles with 5,000 miles on factory replacement engine which was installed 10+ years ago, so car only ran 500 miles per year average since engine swap.

I noticed immediately on test drive that the car seemed low on power. Doesn't have the punch that my last two 964 cars had. Very noticeable lack of top end power.

I also noticed a slight hesitation about 3500 - 4000 rpm when slowly applying throttle.

Finally, the car does seem to take an extra second or two to fire up when warm and an idle that takes a few seconds to settle down. Cold starts seem ok.

My very first thought was secondary distributor belt. Nope, car runs fine with either coil control module unplugged, so dizzy belt must be ok.

My plan is as follows, doing one at a time and checking status of issue:

1) Replace DME relay
2) Replace O2 sensor
3) Replace distributor caps and rotors
4) Replace coils
5) Replace coil control modules
6) Replace spark plug wires (No light show in the dark. Haven't tried the water mist trick yet though)

Any other thoughts before I go crazy replacing good parts?

Thanks for the help guys

Oh, requisite photos of new car

klr10

Stuck / non operational resonance valve?

MikeP.

Worn section in the air flow meter?

Goughary just checked mine in the Suspension Madness thread. Mine was fine; was a precautionary "while we're there" check.

Porschenut_Lee

Thanks guys, I'll start here first before replacing parts.

Porschenut_Lee

Well, my plan was to replace one part at a time to see if I could isolate the issue. The car is parked for the winter and I haven't had an opportunity to run the car on the roads, so I decided to just go in and do an ignition system overhaul and some other preventive maintenance with hopes that come spring the power and hesitation issues will be resolved and she will be ready to go.

So far I've done the following:

1) Replaced DME relay
2) Replaced distributor caps and rotors
3) Replaced coils - Went 993 upgrade route
4) Replaced coil control modules
5) Replaced fuel filter
6) Replaced air filter with K&N for the extra 1 HP
7) Removed and cleaned ISV
8) Removed AFM to check that the zip tie plug wire TSB had been performed (thought this might be my issue)
9) New rear decklid shocks since the airbox on right side and heater duct on left side were removed and space was wide open.

Next on list:

1) Replace O2 sensor
2) New front brakes. Rotors and pads are almost brand new, but rotors have warped.
3) Replace spark plug wires. A couple wires have outer casing chewed on by mice. All others look ok. Is there a patch I can use over the chewed wires to push off this task for a while? I'd like to hold off until next valve adjust if possible since it makes sense to do both at the same time.
4) 993 Motor mounts since the original 964 mounts are toast. Don't know why they didn't do this when they replaced the engine.
5) Install cup pipe and primary bypass - Good time to replace O2 sensor
6) Install Lightweight flywheel and new clutch when current clutch gives up on me. Have parts ready to go!

Once the car is running like a top, if funds allow I will go after a suspension refresh. Goughary's suspension madness thread has inspired me. Going to take a while to recover from the money I am presently dumping into the car though! It adds up quick........

Porschenut_Lee

I just remembered I wanted to check this. Can someone confirm the following for me:

Primary distributor is the upper closest to the fan
Secondary distributor is the lower unit, closest to the heater duct
Primary coil is forward most coil (closest to front of car)
Secondary coil is rear coil (closest to back of car)

It looks like whoever messed with these previously hooked primary distributor to secondary coil and and secondary distributor to primary coil.

If this is the case, what are the issues prior short term, or any long term issues I need to concern myself with. Could this have been my issue from the beginning?

EDIT.....I think the wires were going to the correct coils, just II labeled wire running from secondary to secondary and I labeled wire running from primary to primary. Per the diagram sticker, the I labeled wires are supposed to be for the secondary and the II wires for the primary.

FeralComprehension

I could be wrong, but I don't think that would matter anyway. As I understand it, the channels are identical in terms of the coil/ignitor/etc, and the both are fired at the same time so it shouldn't matter which coil fires which distributor.

Porschenut_Lee

Thanks Feral, that is also my assumption but I don't know for certain and figured someone here might be able to shed some light. Appreciate the input

ThomasC2

If you move the throttle by hand in the rear, can you see that the axle pushes the WOT switch all the way? On some cars now the little rubber **** splits so it just rotates on the throttle axle instead of pushing on the switch.

Duck

Were the above done and still seeing the hesitation? The interesting part is that you are seeing it around 3500-4000 RPM's and sounds like when you are not pressing the gas pedal to WOT. If you had a computer (Bosch KTS300, PDT999, Durametric, Scantool, Bergvill F/X scan tool, etc.) then you could easily check if idle and WOT switches are working. You could also do other checks of the sensors.

I did also do the 993 coil replacement and I noticed the slightest of hesitation at 75 mph on the highway. I cannot isolate it to that as I just had a full rebuild and changed out so many parts at the same time including the crank sensor to the newer version. My car is at the shop getting an oil leak fixed from the rebuild (either cylinder base o-rings or case bolt o-rings). Hopefully getting it back soon and hopefully the hesitation will be gone. Otherwise I will be doing the same as you and switching parts back till I find the issue.

Best of luck.

Porschenut_Lee

Duck,

Those items in the list have just been done last weekend and this weekend. I have not started or driven the car yet to see whether the issues remain or are resolved. I'm hoping resolved, but we will see.

Thomas,
That is a very good point about the WOT switch as when I depress the gas pedal all the way, it feels as though there should be more to go. The car just doesn't feel like it is getting enough air/fuel to get that punch I am used to with these cars, especially in the top end range.

Will look into that! Thanks guys

Porschenut_Lee

Got the car on the road today after doing the items listed above.

1) After the dealership did my valve adjustment right before I put in storage for the winter, my idle after coming to a stop would come way down, then rev up, then drop down low again and stall. The issue still remains. Idle wants to dip, then engine revs to compensate and then drops down and stalls. Embarrassing today as my battery was also flatlined and I blocked an intersection twice as a result and had to boost with my battery pack. Did I not clean my ISV well enough? Why did this issue present itself after the valve adjustment?

Edit: car will start and idle fine, but as soon as I blip throttle, the idle drops and engine revs to correct but then idle dips and engine stalls.

2) Lots of vibration though the engine. Never noticed this before. My mounts are shot, but this makes me think I have a misfire somewhere.

3) At one point rolling through a green arrow in 2nd gear at about 2500-3000 RPM with light throttle the engine hitched as if it got a sudden instant surge of power, but only for a brief fraction of a second. Happened twice in quick succession then never happened again.

4) Checking my new 993 coil upgrade, I pulled the modules for each coil and car starts and idles fine with either pulled.

After doing all of the ignition parts replacement I didn't expect these issues to persist, or new issues to present themselves. Any other thoughts guys?

Goughary

Do a throttle adaptation w a pdt999

Put a multimeter on each plug wire and test them to be sure the resister in the ends on any aren't dead. They should read at or close to 3ohm.

Clean the isv again.

Check for vacuum leaks.

Then look for hall sensor issues.

Clogged fuel filter maybe? Fuel pressure regulator?

Duck

Could the shop have connected a spark plug connector to the wrong cylinder?

540964

Steve Wong told me this is a very common mistake. To check it, shut off the car, unplug one of the ignition control modules (at the coil) then start the car. Do this for each control module. The car should idle and run fine on each. If it doesn't run correctly on one ignition system then some plug wires are crossed.