Pyzik

Hi , I recently took my car to mechanic beacouse i couldnt get it started and I have been told I will need a new icv soon, ( they said it was stuck) so I ordered one used and after installing it the car won't start , just like before I took it to mechanic . So I installed my old icv and won't start eather. The mechanic told me that I might need to tap it if it ever gets stuck again but that didn't do anything . One time car got to run ( bearlly , some poping and rpm around 300 maybe 400 ) so would this be still icv. Problem? Is there a way I can check the icv ?

SQLGuy

All the idle control valve does it add a bit of air, under computer control, to allow the car to maintain correct idle regardless of load (up to a point), temperature, or altitude.

If you were to remove the ICV from an otherwise properly running car and plug the hoses, the car would still run fine, but you would need to press the throttle lightly to start it, and if you let off the throttle completely, it would stall. Other than those issues, a 928 without the ICV would run fine, have normal power off idle to full throttle, etc.

The symptoms you're describing don't sound like ICV. They sound like a maybe fuel pressure problems (like a clogged fuel filter or bad fuel pump), a bad MAF, or maybe a bad wire set, coil, or cap/rotor. A bad LH (like not firing half the injectors) might also result in issues like this.

A metric fuel pressure gauge can be used to check fuel pressure. Ignition can be checked by a visual inspection of components and checking for spark at plugs with a timing light. Pulling and inspecting the spark plugs should tell you if conditions are different between cylinders.

In short, I think some diagnostic work is called for, rather than shotgunning. The one exception to that recommendation would be if you know someone nearby with an '85 or '86 car that runs well, who will let you swap MAF, LH, and EZF to see whether any of these items cure things. If you have known good examples of these items, it's easier to swap them than to diagnose down to them.

Lizard928

On your year adding air during starting is dangerous due to the fact it adds a bunch of timing to the engine. This can lead to the end tanks popping off.

If the car isn't getting enough air it won't start.

Then again there is brittle wiring, the MAF not being in place etc.

So for anyone to say that yes the ICV is the problem is not possible without further diagnostic

Pyzik

I did increase fuel pressure to 58psi for the porken s300 chip, and it ran "ok" hour before switching the icv, the mechanic that told me about the bad icv did diagnose the car and they are very reputable Porsche service . I turned my mad down from 542ohm to 382ohm. Could I have a vacuum leak? I have installed the torque rings too during the icv job.

SQLGuy

A vacuum leak could make it run rich and give you a high idle, but not normally keep it from starting. Is it flooding? Did you look at the plugs?

How long ago were all the other mods done? How long was it running well before it suddenly couldn't be started? How's the battery?

Pyzik

It all started when I I installed the porken chip. I'm am not saying that the porken coused this! The car started and ran really well with it but. It would idle lower than 1600rpm , after trying to adjust idle screw and co screw car wouldn't run at all ( just like now) then I had it towed to the Porsche service people and then got it running by. "tapping" on the icv and told me it would cost me 1000$ at their place o have it changed and I should think about changing it soon , so I got a used icv on eBay for 25$ from 95 BMW 325 and the model numbers are the same as on mine , so I installed it and car won't run , it starts rpm goes to maybe 1200 and then dies. I turned the co screw to original setting(543
2 ohms ) and idled roughy at 200/300 rpm . I switched back to my original icv and it won't run eather, if it does make difference ( I thought it doesn't ) and I just tried starting the car with out. Top part of the intake that connect to the long intake tubes.... ?!?!? Help

Pyzik

so how do I add air ? Maf rebuild? Should I make vacuum leak to see of it idles?

Pyzik

I recorded a video , maybe that will help to understand what's going on . My battery I little weak from cranking ... http://www.youtube.com/watch?v=h2bc3uFfDzk

Bill Ball

That video helps a lot. So, your car seems to start just fine, but then it dies immediately. That's far different than not starting at all. Is the fuel pressure still up after it dies? It sounds to me like the ignition or injectors signals are being cut-off as soon as you release the key from the start position. On S4s if the crank position sensor is bad, NOTHING happens (except the starter cranks - no fuel, no spark). I'm not sure on 85s if that might be different. However, I think they are the same in this regard, so that's probably not the cause. LH brain failure would be one possible cause, as you have fuel and spark while the starter cranks. Do you have a buddy nearby with an 85/6 so your could swap LHs? Or you might swap the stock LH chip back in. The ICV isn't causing this. The car would start and run but idle lousy.

Mrmerlin

the ISV is a consumable part buying a used one should be avoided ,
the internals of them wear out ,then they stick in a certain position.
you should go through the system
rebuild the MAF,
replace the ISV with a new part,
replace the O2 sensor use the factory replacment,
replace the crank sensor.
replace the 4 running relays,
EZF, LH, fuel pump, ignition
these are all 53 relays

since the car isnt running properly these are all things that will cause it to run poorly or not at all, swapping in used parts is a recipe for a tow truck to show up.
I had a car here and all of these parts were bad, so yours could be the same .( it also had a bad LH)
Once all of these parts were replaced the car ran perfectly.

If you want the car to run for a long time reliably then dont cut corners,
if you dont have the cash then save till you can fix it properly

Pyzik

Today I disconnected the maf and the car started right up and idled at 2000rpm with the maf disconnected , so I'm sending my maf to to get it rebuild . Thank you for all your help!

Pyzik

So I recived my maf from rebuild and plugged it in( checked the ohm before installing and it was 382ohm) and cranked and same thing is happening, starts and dies a sec later. And if I hold gas it revs but two seconds later it dies . And if I unplug the maf the car runs at 2k rpm no problem. I would like to take a look at the throttle body but I'm not sure how to take the t piece out of the plenums. Would I have to adjust the idle after maf rebuild? I will try asking a local guy that drives a 86 928 for the LH to swap . Also hen I was at the mechanic a month ago , he said. That " my knock sensor was disconnected because. The plugs fell apart , so they hooked it back up for me . I did t know my year had knock sensor I told him , would plugging it back in cous anything?

Pyzik

Also I think something was draining the battery for the last three weeks and seems like this yellow optima from 3/11 is no good anymore as I tried charging it for 10 hour and I didn't do anything! And in winter I wouldn't start the car for a month , and I could start it Easly.

PorKen

Get a new Idle Control Valve. Unlikely to find any good used ones. They wear out.

If the 3-prong connector for the 'knock sensor' was at the rear of the engine, you need a new Crank Position Sensor. You may have disconnected or disturbed the 'repair' when installing the used ICV.

If the connector was at the front, you need a Throttle Position Sensor extension wire. It may be wired incorrectly.

Pyzik

The connector was in front by the diagnistic plug