rsqrd

I have been having the recently weird problem on my 88 928S4. 120K miles, and just recently, driving along, about 10 minutes or so into the ride, the engive will drop to idle for a short time... 2 - 10 seconds or so. 5 speed, so you feel it of course. Then it comes back on, no problem.

Checked the 'easy to get to connectors', new fuel filter just in case, I don't thin kit is a fuel cutoff cause it drops to idle, doesn't stall. Once, I think when I went into neutral it seemed the idle was hunting a bit, but ...

Before I take off the top of the engine to look around, anyone have a similar experience or point me in a reasonable direction? I thought maybe the idle throttle switch could be it. You know, if the brain thinks the pedal is at idle, then it forces the engine to idle? Does that even make sense. You can stare at wiring diagrams until the trace goes into a big box with a transitor symbol on it... ha..

Let me know if anyone has a good starting point.

blitz928

Has your LH computer ever been rebuilt?....and by the way...Welcome to Rennlist.

rsqrd

Unknown, I got the car a few years ago, but I am only second owner and forst owner was meticulous, I have all records, dealer serviced, don't see that listed.
Been around Rennlist for years... 911, 930, 928S and now the S4.

Heck, occasionally I get advice about the Ferrari.

rsqrd

Hmm. it says new user, you are right. I think I have two accounts for some reason, have to check into that.

rsqrd1

How did this happen. I feel so.. dirty. Gotta kill this other account

Mrmerlin

welcome,
old timer
it appears as though one of your accounts is worth more than the other.

For your car I would start by cleaning the battery connections,
then the hot post connections.
Also remove all of the fuses and clean the ends with a pencil eraser then do the relays , smell them for burning any burns they need to be opened,
Look above the CE panel for water telltale drips this will give you an idea if you need to do a blower box reseal.
928gt.com for a fuse/relay chart on page 2 under tips and links print one off to keep in the car
Remove the connectors for the computers to see if they are corroded.
Remove the aircleaner and inspect the MAF and ite other wire connectors under the intake.
Also inspect the hall sensor connector and wiring across the front of the engine (Hall sensor is in the backside of the passenger side cam pulley housing)
Report back with any findings

John Speake

Welcome ! Lots of help here to get to the cause of your 928s problem.

If there is no banging or popping in the exhaust when the engine picks up again, I would speculate that it is a cut out of injector pulses that is the problem, rather than an igntion cut out.

One common problem is a short circuit on the connector one of of the injectors. Pull off each one in turn, pull back the boot and check for bare wires that could touch. If one shorts, then all injectors are cut off.

If all seems well in that department, then see if you can borrow a known good LH ECU, or send your LH to a kindly RL memeber who if willing to test it in his car.

Mrmerlin

more reading, before you begin replacing parts.
https://rennlist.com/forums/928-foru...light=tps+test

rsqrd1

Ok, reporting back.

For your car I would start by cleaning the battery connections,
then the hot post connections. BOTH GOOD
Also remove all of the fuses and clean the ends with a pencil eraser then do the relays , smell them for burning any burns they need to be opened,DONE AND GOOD. EVEN REPLACED THE FUEL PUMP AND BRAIN RELAY.
Look above the CE panel for water telltale drips this will give you an idea if you need to do a blower box reseal. NOPE NO DRIPS
928gt.com for a fuse/relay chart on page 2 under tips and links print one off to keep in the car GOT THE ORIGINAL THAT CAME WITH CAR.
Remove the connectors for the computers to see if they are corroded. CLEAN
Remove the aircleaner and inspect the MAF and ite other wire connectors under the intake. LOOK OK, BUT SEE BELOW
Also inspect the hall sensor connector and wiring across the front of the engine (Hall sensor is in the backside of the passenger side cam pulley housing) NOT YET

It was suggested that I look at the Crank sensor, so I pulled it and it was dirty with a thin layer of black grease, so I cleaned it. The face wasn't smooth, but had a tiny sharp dent? I couldn't tell if it had been penetrated.

Anyway, took it out for a drive, and while it didn't do the cutout trick( of course this was intermittent anyway), it did do something else: Get on the throttle (4k rpm) then lift foot off accel and push in clutch. Car RPMS drop to ALMOST zero (no stall) then hunt back to 5-600 rpms.

Did this a few times, then it just started working better. Same test, dropped to 800 rpm rock solid idle. Then a few times later, once when I wasn't on the throttle, dropped to zero then it stalled. Started right up again.

I'll check the Hall on the pass side today too. Still weird.

Mrmerlin

You need to read the link i posted test the TPS switch at the computers, inspect the wire harness that goes to the TPS under the intake, make sure no broken insulation and the pull the connector off and see if its clean

AO

I'd check all your ground points, including the two posts under the air filter on the block (had one of those bite me in the *** once). You may also want to check for vacuum/flase air leaks.

rsqrd1

Decided to do the little test of the TPS from the book. pins 2 & 5 on the connector, register correctly. Pins 3 and 5, not so much. Read Infinite Ohms no matter the throttle position. How easy is it to check the TPS directly. Do I need to disassemble the engine. But I suspect this is the problem?

John Speake

2 & 5 are for the closed throttle switch, so you say that is OK. 3 & 5 are the WOT switch, they often fail but that will not cause the cutout problem you have. Leave it for now.

Suggest you become a RL memeber, best value for money you will ever get !

Enter location and car details in your signature. Maybe someone local to you can test your LH in their car, once we know where you're located.

rsqrd1

Actually am a member, somehow got two accounts, rsqrd1 is the live one.

Ok, I thought that might be the case on the WOT side, except the idle hunt was most pronounced when I went from WOT to idle. Would that make a difference? Like how could I be WOT and idle at the same time (or vice versa?) would this confuse the box.

rsqrd1

Going to read this now. Overlooked this message, good idea, esp cause my readings aren't normal.