doruiacovescu

Hello!
My 90 c4 is showing me the check engine light after hard acceleration. After some time, if i drive normally, the light will go off by itself. i do not have the acces to a scanning tool and the only porsche service has the hammer broken...
Any thoughts?
Doru

Paulie964

I don't know for sure, but I have a similar issue. If I don't let my car warm up before i drive, I get a check engine light that goes off after a while. My mechanic tells me its nothing serious ...

Has to do with moisture accumulation somewhere around (or in) the cylinders ... wish I could be more help ...

Does this happen even when the car is fully warmed up?

doruiacovescu

yes, even if the car is fully warmed up.

Paulie964

I may be wrong, but I think there is a way you can check the code yourself without a scanner tool ... it involves watching your check engine light as it blinks dots and dashes ...

search ...

ValveFloat

Here is a link to the CEL code technique, might not work on your '90 though.
http://members.rennlist.com/billwagner/CheckEngine.html

My car was setting a CEL under load when I had an Autothority chip. Switched to a 911chips, and its fine.

-Joe

Jonnygo1

I've got a similar problem

doruiacovescu

No chip installed on my car and no, the flashing technique it s not working in my 90 car.
Doru

Erik@GBox

I was wondering if this might be caused by a bad O2 sensor? I am curious to hear what this ends up being, but you might want to consider checking that out as part of your diagnostic/problem solving.

Erik Johnson

doruiacovescu

Thanks, need to do a lot of checks because of the lack of the hammer. But could it be related to o2 sensor? I understood that the o2 sensor is ignored when car is not at idle... Or i didn't understood correctly?

Mr.E

It is related to the O2 sensor, but does it by chance happen at around 4500 rpms?
If so, it can be related to your resonance valve/flap. If so, it may be a vacuum issue, or a poor electronical connection. Check your vacuum lines up top, or if you're ambitious, take off the intake filter and right side intake, and manually suck on the vacuum line to your resonance flap to make sure it's functioning properly, and while you're at it, check the vacuum lines and connectors for leakage.
Also check the connectors up top, might as well check them all, and clean up any corrosion.
The check engine light is an emission related "idiot light" and will not tell you of pending engine doom, so your mechanic is right in telling you things are OK, but you do have an emission related problem.

Hope that helps,
Eric

doruiacovescu

Hello!
THanks for that. Unfortunatelly i do not how do that, i do not know at what valve are you reffering to. And yes, it happnes at about 4500 5000rpm.
When you say electrical are you reffering to big$$$Beru wires or small electrical connections from the wot idle switch etc?
Doru

doruiacovescu

Well, checked it finally with a hammer and it shows that knock sensor signal is unplausible. Cleared the error and now it s gone... for the moment i think. Do i need to change the knock sensor or just clean the contact?

Rocket Rob

I had a knock sensor fault once. Removing the electrical connector, cleaning the contacts and reinstalling was all it took to fix it. Give it a try, you may be equally lucky.

Paulie964

im not trying to highjack the post, but you guys got me thinking about my car ...

when my 964 is not warmed up, it drives funny. When its completely cold, the throttle will have a delay (sometimes) ... at about 2300, it will surge/jolt ... fully warmed up, it runs like a champ

perhaps the O2 sensor is not fully warmed up?

Cupcar#12

O2 sensor is not used for startup on the 964. Only once the car is running does the DME take inputs from the O2 sensor.

most warm CEL issues are O2 related (signal unplausible on the hammer), try changing your O2 sensor

start up issues can have a number of causes, is it a daily driver?, does it sit, low mileage or high?

I would do (in this order, assuming you have a stock chip if not repalce the stock chip and most likely it will go away)

1) valve service, oil change, filter change (i.e. normal 15k serivce)
2) Fuel filter replacement
3) replace O2 sensor (20 minute job with hand tools)
4) ISV
5) check Catalytic converter - could be plugged/dead, small bts will start falling out of it in this case.
6) injectors flow clean and flow match.
7) ? ?