Bertrand Daoust

+1 on the FP relay.

If it has never been changed, it's a good thing to change this one and few others (FP, LH, EZK, and starter) as preventive maintenance.
There're not expensive.

Ramp

I cleaned all the relays when I bought the car a bit under 2 years ago but have not replaced any. Will give it a try. I would not have thought relays would be 'tempermental' like this and would tend to either work or not.

Jason89s4

+2 on relays. Change all three "53" relays. Throw the old ones away (so you don't use them again). Cheap, cheap insurance and elimination of that as an issue.
I don't think you did, but have you unplugged the MAF and then started the car? Does it act any differently?
-Jason

Ramp

Changed the fuel pump relay yesterday so just noting time on the thread. (Jason - good idea to throw them out - I do tend to keep old stuff). So far all good but the problem is intermittent. Time will tell. Now onto the window issue that just popped up.

Thanks

Ramp

So it's not a faulty relay. Since changing the relay last week, the car has been sitting in the garage while I fixed the window motor. Started right up this morning, idled perfectly, backed out of the garage, added gas, stall. Start right back up, idles, add gas, stall. Wait 30 minutes while doing other errands, start, idle, pull away, all is fine.

With this happening intermittently, it's the one major issue keeping me from enjoying the car as I don't have reliability.

Next recommendation ? Here's what I said in post 14 -- "What should be next logical step ? Send in the MAF for testing and calibration or change the O2 sensor first ? Do MAF's go out of range with this low mileage ? I cleaned all the connectors and cleaned the wire during the intake refresh. Also, this is an occasional issue as the last time was about 3 months ago and has been running nicely all summer."

Ramp

Just to be sure, the fuel pump relay is a standard 53 - correct ? I saw a post on an earlier car that said - - "Bridging 30->87 should run the pump ALL the time, which is not safe. A 53 relay will do this, but it should only be a temporary fix"

Mrmerlin

If your MAF is old have it rebuilt then adjust it when you refit it
do a search for adjust your MAF by mrmerlin
replace your original o2 sensor as well

928NOOBIE

All above and see if the idle bypass screw could use some attention; remove it all the way and clean it.... you won't believe how gunked up that thing can get. It may just need a little more air to keep running when it goes into gear....something to try and cleaning the valve will do nothing but help and it's easy/free.

Screw it closed all the way (to the right) and track how much to turn it all the way closed so when you re-install you can make sure it's back in the same position and if you stil lhave issues maybe go counter clockwise (giving more air) an eighth of a turn and see if that helps. The idle bypass screw is more sensitive than you think so make adjustments in very small amounts and then test drive.

dr bob

The fuel pump relay on your car is indeed a "standard" 53b Bosch relay. The LH controller triggers the relay when the key is on and engine RPM is detected via the Crankshaft Position Sensor (CPS).

The reference for early cars refers to the fuel pump relay that has the RPM detection built in. The CIS cars particularly have this style relay, where there's a separate dedicated contact (31b) for the tach signal. Some folks will plug in a more standard relay that doesn't include RPM detection, so the fuel pump runs whenever the key is in position II or III (engine run or engine start). That bypasses a safety feature in the original relay, intended to shut off the fuel pump if you get in an accident that causes the engine to stop but you can't or forget to turn the key off. The fuel pump whirs away, happily pumping fuel to feed the growing fire under the hood. I think there should be a mini-Darwin award for folks who do this for more than testing purposes.

Christopher Zach

Why am I thinking this is a faulty ISV? Have you pulled it and checked to see if it moves in both directions smoothly when applied a limited current power amount?

Brett Jenkins

I am experiencing similar issues on the 86.5 I bought last month. I just got the car started and back on the road, but it is way down on power and feels like a 4 cylinder. At first, it was only after warming up, but now it's after a cold start as well. Even though the car only has 54k miles, it had been sitting for a very long time. All ignition parts were replaced, as well as TPS, ISV, O2 Sensor, CPS, fuel pump and filter, battery, all fuel lines, vacuum hoses and rubber hoses under the intake, all intake boots. Injectors were bench cleaned. I replaced all "53" relays and all fuses, cleaning as I went.

I tested the temp 2 sensor and it seems to be ok, also tested the wiring continuity back to the ECU. I swapped out the MAF for my known good spare. I have verified all plug wires are installed correctly and all are firing as expected. I repaired one injector connector early on, but am I correct in assuming if there is a injector wiring issue, it would be an all or nothing situation?

I am looking for possible problems and where to check next? Bad or intermittent LH? Clogged exhaust? Harness wiring problem? Fuel pressure regulator or dampers? ground points? What else to check?

4664

Was it ever established what OP's problem was back in 2019?
I have had the EXACT same issues on an unrelated vehicle: "After she's warmed up, if I make a stop, she will start right up and idle fine BUT give it any gas and she stalls unless you feather. Put her back in neutral and she idles fine. Let her sit for a while, issue goes away."

In my case it ended up being a fuel line restriction with gunk/debris partially blocking the line.

Christopher Zach

How about the spark computers/amplifiers on the front? My 944S was a basket case for 2 years till I replaced it, and when I got my 86.5 928S home as a nut case swapping those out made it run happily......

928NOOBIE

FPR and dampers....if they are original chances are they are all leaking and not working correctly.