'88 Carrera 3.2 shuddering problem

[Synchromesh]

I'm working on an '88 Targa that has been sitting for about 15 years. Lots of things have been done in the last few months. This is the engine stuff already finished:

1. replaced a bunch of oil and fuel lines
2. oil + filter
3. alternator belt (and removed AC compressor)
4. valve adjustment
5. O2 sensor
6. head temp sensor
7. adjust the 2 flywheel sensors with proper gapping
8. spark plugs and wires
9. dist rotor and cap
10. SW chip + solid state DME relay
11. Seafoam to clean the system first, now Chem Tool B60 to clean it further

Basically the engine runs relatively well but continues to have these issues:
1. idle is a bit high (usually at around 1000 rpm) and unstable with some dipping and hunting at times
2. not enough power
3. there's a noticeable shudder/lag in all gears between 1000 and 2500rpm. This is especially bad when shifting into gear from coasting

Any suggestions?

[Schulisco]

Did you measured the amount of fuel to be delivered as said in the specs?
High idle might be a vacuum leak. Check the vacuum system with a smoke tester. This also may the reason why the engine shutters on low rpms.
I would replace the 2 flywheel sensors to make sure that're not a possible source for issues. Their plastic housing may break over time and they will corrode then for sure.

Thomas

[wazzz]

I know for sure someone is gonna chime in and mumble about point 10 of your list. You should probably start with the factory chip if you still have it and a standard mechanical DME relay.

Also, have you set the ICV center point by shorting the test plug? Idle speed for an 88 is about 880.
Can you also test if idle speed drops a bit when you open the oil filling cap? This should be the case.
Also check both throttle switches. One is the idle switch that should be closed when idling and the other is the WOT switch which should close at about 80% of throttle and beyond.

[NotStock]

Been down this same road recently. As pointed out, smoke test and fix every vac leak you find. I bet your idle drops to where It's supposed to be and smooths out. Mine did. Massive leak at the hard line to the brake booster.

As for the power, you haven't touched the injectors yet. Run the car and start checking the exhaust flange temps with an IR gun. I imagine you'll find one or more that are colder than the rest. Likely that you have sticking or somewhat plugged injector(s). Move a known good injector to that hole and see if the problem follows the injector. Your flange temps should be roughly the same. Best way I found to diagnose misfiring cylinders.

I did a few rounds of this and found bad injectors and bad plug boots on mine.

[Tippy]

Spent 6 months chasing an exact gremlin never figuring after replacing nearly everything and went aftermarket EMS.

Worth it in the long haul I feel, but a steep learning curve

[Synchromesh]

Thanks guys. Lots of good points here. However...

Originally Posted by NotStock

As for the power, you haven't touched the injectors yet. Run the car and start checking the exhaust flange temps with an IR gun. I imagine you'll find one or more that are colder than the rest. Likely that you have sticking or somewhat plugged injector(s). Move a known good injector to that hole and see if the problem follows the injector. Your flange temps should be roughly the same. Best way I found to diagnose misfiring cylinders.

I did a few rounds of this and found bad injectors and bad plug boots on mine.

That's where I'm probably going to start. I think the car has been sitting for quite a long time so I'll see if bad injectors are the problem. After that I'll start chasing vacuum leaks and throttle position sensors.

[scarceller]

Very first test I'd like you to do is observe cold start as follows:

- Turn key to RUN but do not start engine yet.
- Is the idle control valve in the engine bay humming and vibrating. If so continue.
- Do not touch gas pedal for remainder of these test points
- start engine, it must initially idle at 1100-1200 RPMs
- as it warms over next 3-5 minutes the idle speed must start dropping. Do not touch gas pedal
- After 3-5 min it must idle at around 900RPMs

If the above functions as outlined then we know the idle switch is closed at idle and the idle control valve is functioning and the DME has the correct ability to control idle speed.

If the above test fails we have an issue with idle switch and/or Idle Control Valve ICV.

Also observe what the engine does at initial cold start, does it hunt up and down for idle speed? If so it's indication that mixture is set rich.
Or does it sputter and cough at initial startup? Indication of lean mixture.

Please start with this simple testing, no tools required

I suspect your idle control valve or idle switch are not controlling idle properly. One step at a time I'll help you diagnose.

[scarceller]

HINT: stop throwing parts at the problem, usually this makes things worse. Often the trouble is that you have more than one problem. You need to diagnose carefully and prove that a part is faulty.

Also, if you have no cat converter please unplug the stock O2 sensor and leave it unplugged till we figure out the problem.

[wrxnofx]

Originally Posted by scarceller

HINT: stop throwing parts at the problem, usually this makes things worse. Often the trouble is that you have more than one problem. You need to diagnose carefully and prove that a part is faulty.

Also, if you have no cat converter please unplug the stock O2 sensor and leave it unplugged till we figure out the problem.

All awesome advice, Sal! Shooting the parts cannon at a symptom is an exercise in futility. And expensive.

[NotStock]

Originally Posted by scarceller

Also, if you have no cat converter please unplug the stock O2 sensor and leave it unplugged till we figure out the problem.

Should the O2 sensor be unplugged at all times when running without a cat?

[scarceller]

If you do not run a cat, the engine runs best with O2 disconnected so long as mixture has been properly setup and everything in proper order. In Open-Loop mode (o2 disconnected) the DME runs much like the Euro engines do.

[Synchromesh]

Update: I was about to send out the injectors for a cleaning but before I did that it solved itself! I believe one of the injectors was dirty which caused the hesitation but basically after about 2-3 hour drive (with a lot swearing) the whole thing actually seems to have healed. There's not more hesitation at any RPMs and the idle is solid and stable. Whatever it was, Chem Tool seems to have done its job. I'd like to thank everyone for advice as well.

Of course, after this the voltage regulator had some issues sending 17V to the battery but it's a whole 'nother story. Already fixed it, running like clockwork.

Originally Posted by scarceller

HINT: stop throwing parts at the problem, usually this makes things worse. Often the trouble is that you have more than one problem. You need to diagnose carefully and prove that a part is faulty.

Eh, I wasn't throwing parts at this particular problem per se. I was just replacing things I figured would need replacing after sitting for 15+ years. O2 sensors rarely last too long and the head temp sensor actually returned infinity during a test so they had to go. Rest is just part of waking the car up and preparing it for some exercise.

[911obgyn]

Nice italian tuneup worked!
Now keep driving it.

[Synchromesh]

Yes it did! And yes I plan to drive quite a bit.

[Dave Kost]

Synchromesh- What Chem Tool did you use?

[Synchromesh]

Originally Posted by Dave Kost

Synchromesh- What Chem Tool did you use?

It's in the first comment. The B60 injection cleaner.

[Mr. Merk]

It certainly wouldn't hurt to have the injectors cleaned and tested. I haven't tested a set yet that sprayed correctly before cleaning.

I replaced my original fuel lines and did the injectors and adjusted the CO mixture. Car runs better than it ever has over the last 70,000 miles of ownership. Record MPG going to Rennsport and back last year.