kmascotto

Here are some more "before refresh" pics that show vacuum lines.

kmascotto

And more pics of the after refresh look: It sure runs smoother

MainePorsche

Sounds like the ISV is on its way out. Mine started with the same symptomatology, and then progressed to poor starts/running even when warm. You'll have to 'pop the top' to replace it, and WILL replace all vacuum lines to new while there. Important to check the status of all rubber union connectors on the vacuum lines. When refitting vacuum lines I placed a small amount of the pliable 80060 Permatex gasket sealant on the hardline away from opening of the hardline. When I then fit it into a its rubber connector it acts as a sealant and keeps it in place.
Fuel system - check for smell of gas at the vacuum line to the dampener/regulators. If smells like gas, that piece will have a faulty diaphragm inside. This however would give symptoms even when warm. How's the fuel filter ? When last replaced ?
Faulty Temp II sensor can cause your symptoms, but these are simple and robust. I forget the resistance values at temperatures, but the WSM has them. I would check it to be thorough.
It is most likely the ISV.
When you do 'pop' the top', don't forget to change upper and lower O rings for the injectors. The lower ones are especially under much stress.

FiveElements

Ok.. so Bill Ball came over with his 89 car. We connected a diagnostic system up. The car started up cold and idled at 1400 rpm for a while (30 seconds ish) then down to 900, than after heating up to about 100•F, the engine stalled. Then we started it up again no problem. It idled at about 900, then jumped up and down with idle and stalled. We checked the diag computer and NO errors were found. We activated the idle control valve manually using the computer... it clicked loudly open and closed. We tested the throttle switch and all was showing good.

So Bill and I swapped his MAF into my car. His is rebuilt recently and his car runs perfect. The new MAF made car run worse. It stalled constantly. It idle at 500 to 700 for only seconds and stalled. We had to keep our foot on the petal to keep the car running. After the car reached full temp, the car ran fine with his MAF. We put my MAF back in and the car ran perfect still.

We took sensor reading from the temp sensor on the water neck passenger side. It was 336 ohms on each pin. Car was about 170•F. The book said that was correct.

Bill and I are totally stumped. Your thoughts?

Leon Speed

Did you try swapping the Ecu? Split hose between ISV and MAF boot?

Randy V

Erratic Idol!!?? Not another singing talent show!

MainePorsche

Was going to suggest the swap trial. Didn't think of the split hose down under. Good call Aryan.

Mrmerlin

NOTE simply swapping the MAF wont make it run better,
you also have to do a battery disconnect so the computer will relearn the new MAF parameters.
this applies to 87 and newer cars.

I would suggest to install a new temp 2 sensor and connector ,
there is a possibility that the wires are shorted together.

Check the computer connections for corrosion spray them with Deoxit .

Clean the battery terminals and the wires that are connected to them.

Clean the 2 ground points at the rear of the V these are for the FI harness

FiveElements

So that's probably why the switch of the MAF made things worse. If Temp Sensor II is failing mid way during warmup, this would stall the car? That seems doubtful. I doubt poor battery connectors. All is very clean there. Intake tubing are all new and boot to MAF are good. I'm sensing that the MAF is the problem. Probably need to get Bill to bring his car back and we can pull the battery terminal and try his MAF again.

Mongo

It's surprising at how a corroded or loose LH ground can affect running on these cars. I had to replace the ring terminal on the LH one that was corroded. The car would idle fine when cold, but run like complete crap when warm. After the R&R of BOTH the LH and EZK grounds (I figured I'd do the EZK too since I was back there), there have been no running issues at any temperature.

Also, never, EVER overlook the negative ground strap to your battery. There are threads about that one wreaking all sorts of havok in this forum.

MainePorsche

Yep.
MP VIII & IX can wreak havoc if not maintained. They are a pain to access and are not readily visualized. They are also subject to the harshest of engine heat which be itself can degrade the carrying capacity of the wires and unions there. How's your 'V' ? Spotless ? Not a drop of water from the nearby gaskets and regulator/dampener bracket bolts at the back end ?
Only if your POSITIVE your battery ground strap is recent enough to be excluded from the issue would I not replace it. If you do, for kicks cut the insulation off when removed and inspect the condition of the strap.

the flyin' scotsman

did the car have these issues prior to the intake refresh and other work?

interesting to learn what was found/replaced during the intake work.

soontobered84

+1

Easy to access. Easy to test. And easy to replace. A faulty temp II can cause all kinds of havoc as it's tied to the LH computer AND the EZF. Since it effects changes as the temp warms, it creates a changing array of symptoms.

Temp II is where I would start.

alabbasi

May I ask what software you're running?

Thanks

kmascotto

+1