Ricardo Vega

Hey guys, had questions about my current issue that's getting worse by the day. Car is idling rough, dying and not starting without a good throttle of gas pedal. I notice it gets worse as I drive longer. I also do notice that as I'm at a set speed let's say 60 mph, I can feel a bit of jerk as if maybe gas doesn't get out of injectors or no oxygen is getting in car. Obviously that's just what it seems like but why it jerks I don't know. It does get to the point when I'm getting out of a parking lot the car in Drive jerks bad forward and then wants to die. If it's in Neutral it idles up and down like crazy from 1500 down to 0 over and over.

I did recall having this issue months ago for a few days and then didn't happen again till now which has been like 5 months from now.
Now that's it to the point where it can't be driven safely it's maybe best that I use another car.

But my questions is if someone can tell me where I can educate myself about the theory about the MAF, LZK and anything related to what I think is the issue? I have looked up on Google about these issues and it seems it's one of the two but to be sure I want to see how to trouble shoot each.

I also came across a Rennlist posting about the relay for the LZK being replaced with a $12 option and issues go away. Can someone fill me in about how I can find out what's going on?

Also, I did have my chip replaced on my ECU like 2 years ago so I think that's good because from what I know that's what controls the spark, right? Thanks!

Ricardo Vega II
1987 Porsche 928 S4
Black/Plum
125,xxx miles

safulop

Others may be more expert than I on these matters, but your car has two computers, the EZK for ignition and LH for fueling. Neither one should affect the idle in that fashion, that I am aware of. I believe that your problem could easily be due to a bad MAF or the wiring boot for that. My MAF also presented intermittent running problems which seeming "went away" for several months before returning with a vengeance. If I were you I would start by getting a spare MAF from someplace and putting it in, keeping close eye on the wiring connectors as you do so.

safulop

And by the way, the jerking at speed or under acceleration can be due to the MAF sending the wrong mixture signal, which causes the LH to starve the engine of fuel. The result is, as you describe, as if the injectors are not putting the right amount of fuel into the engine. In fact, they may not be, but it is not their fault.

ammonman

The hard starting is often a sign that one of the two fuel pressure dampers or the fuel pressure regulator has a failed diaphragm that is allowing un-metered fuel to get into the intake through the vacuum lines. When you open the throttle to get it to start the extra air thins the over-rich mix down to the point the car can fire up. Pull the vacuum lines of each of the dampers and fuel pressure regulator and see if they smell of fuel. Connect a hand held vacuum pump to each of them and see if they will hold 15-18" of vacuum. If they fail to pass either test then they need replacing.

Mike

jheis

Take a look at the connector for the Crank Position Sensor (under the air box). If the connector is disintegrating (as they are known to do) it can cause lots intermittent problems - until it totally fails

bureau13

I had some similar problems, although idle was not terribly affected, and it turned out to be injectors. Does your problem happen while accelerating, or more when you're just cruising along? If the latter, try unplugging the O2 sensor...if the problem goes away or gets better, you likely need a new sensor. That was recommended for me to test, although in my case it wasn't the solution.

Speedtoys

Another car in need of $2k in top end overhaul work.

Not a bad thing, just something that 30yrs needs done.

Ricardo Vega

I appreciate everyone's input. As of this morning my car no longer holds anything higher than 200 RPM and even when I press gas pedal it doesn't kick up as I press pedal. It hesitates and doesn't rev much higher than it would. And it just dies.
I'll test pressure on fuel pump and maybe remove MAF and have some test it for me.
Thank you.

Ricardo Vega II

Speedtoys

Unplug the maf.

I bet it'll run.

Time for that refresh job...even if its just the maf now, a world of issues lie behind it

Lizard928

Dead/dying MAF is #1 suspect. But if the top end refresh hasn't been done, it is in need of being done for sure.

safulop

Yes, the intermittent nature of the problem, followed by these eventual death throes, is making me think it's MAF rather than fuel pressure. If a problem's history is intermittent, it's electrical not mechanical.

Ricardo Vega

Thanks for everyone's comments. I'll get on it this weekend and have MAF removed and replaced and order the other essentials for the top end procedure. I'll keep you guys posted. Thanks to all my brothers here online.

Ricardo Vega II
1987 Porsche 928 S4
Black/Plum

safulop

^^^^^^^^
My advice, on the top-end refresh, if you think they are very old parts do yourself a favor and get the two intake valves -- meaning the "flappy" intake runner valve (a cheap part that is essential for full power at high rpm) and also the idle stabilizer valve. You will never get a proper idle behavior if that last one is old and frozen -- unfortunately even the "cheap" version is like $225. But it is crazy to bother with taking the intake off and not making sure of these two parts.

Speedtoys

In Rogers spreadsheet documented kit, it comes with alllll of that.

Ricardo Vega

Speedtoys, do you have access to that spreadsheet? Or can you send it to me if you have access to it?

Ricardo Vega