Bulvot

Thank you for the additional information.

It sounds like the Spanner from JDS would be worth the investment. I hope to install forced induction in the not too distant future, and I'll look into the sharktuner at that time.

I agree that throwing parts at a problem isn't the best approach, but I also believe in preemptive maintenance. Since the MAF is certain to fail at some point, I'll go ahead and have it rebuilt. That will include testing, so I'll know if it was a potential problem. While I'm in there, I'll inspect the connections and anything else that is easier to access with it out.

I've gone over the grounding points and power connections and 14-pin connector, so I am pretty sure that those are not an issue at this point.

Bulvot

So....I had a little time to pull the MAF sensor this evening. When I removed the filter cover, the filter looked a little rougher than when I inspected it a few months ago (right before the problems started). It looked a little chewed and had a lot of debris embedded in it. When I pulled the filter out, the screen of the MAF sensor was about 1/3 obstructed by debris. Droppings, seeds, etc. It was definitely not like that shortly before these problems started. I had everything apart when I did the timing belt job and had been driving it pretty regularly after that, right up until it started having these problems.

Anyway, I did pull the MAF sensor out, and it looks to be in really good shape. I know that the cosmetics aren't necessarily an indication of function, but it did look good. On a whim, I cleaned up the filter as best as I could and put everything back together. The car started right up, idled fine, and responded to a couple of light throttle applications. Rather than risk anything else coming out of the filter, I shut it down after that very short test. I've ordered a new filter and will give it a more thorough test once it arrives.

The car is always in a garage and I thoroughly inspected and cleaned everything, including intake from MAF screen to radiator mounted intlets, when I put it back together this past summer. I drove it fairly regularly right up until it started having these issues. Whatever rodent decided to crawl into the intake and make a mess worked pretty fast. And it had many other options for places to explore. I can't imagine why the 928 appealed to it above everything else.

Hopefully this will turn out to be the problem, and there won't be any internal damage from whatever the motor ingested. I'll provide an update once I put the filter in.

Wisconsin Joe

Many folks, including me, run 'critter guards' on the intake funnels.

I use 3/8" Hardware Cloth. It's cut to fit over the funnels and keeps anything 'mouse sized' or bigger out.

Bulvot

That's a really good idea. Do you put it at the end by the radiator, or fit it further in so that it's hidden?

Mongo

A couple things come to my mind. The way it idles was remarkably similar to mine. I put a new MAF and a rebuilt LH from Louis Ott in mine before I noticed two big issues:

- LH and EZK grounds were loose AND corroded.
- MAF sensor wiring had decomposed causing wires to touch.

If you haven't done an intake refresh yet to replace any vacuum lines and hoses, your next culprit could also be the ICV (idle control valve) under the intake. They tend to stick and WD40 down the brake booster vacuum line to it at the "Y" usually tells you whether or not that is the issue.

Lastly, hesitation on acceleration usually means either old ignition wires and plugs, or leaking fuel dampers and pressure regulator (can also contribute to rough idle).


I'm linking a thread I started back in 2010 where I did some serious vetting on my electrical and fuel injection. If your symptoms sound similar, I would recommend checking the thread out. Mind you it's a very long read but it may help chase down some problematic sensors, grounds, and fueling issues.
https://rennlist.com/forums/928-foru...-page-4-a.html

Good luck. These 928s tend to test patience as they get older. Ideally, you will want to tear the intake off and do everything mentioned by others on here since 90% of the time it fixes all the running issues.

Bulvot

Thank you, that is very helpful. You did a lot of work and troubleshooting and I appreciate you taking the time to share it.

I did check the MAF wiring. The cable shielding was split at the plug, but the wires were fine, as were the contacts.

My plan for now is to do the minimum to get it running since I have another major project underway. Then, later this year, I'll do a full intake refresh and replace anything else that makes sense at the time (ICV, MAF, LH, etc). Of course, if it turns out that I can't do something relatively easy to get it running now, then I'll have to do all of that much sooner, but also much slower

SeanR

One cool evening and a determined rodent can build quite the nest on top of the filter and do some serious damage. Odd running conditions on any car with a MAF, that's the first place I look.

karl ruiter

One simple thing to always check on a rough running 32 v car is to pull the plug wires and make sure the ends are not oily. If the cam cover seals around the plug holes are leaking you can end up with the plug well being an oil bath for the plug.

PC-85-928S

My car was running very rough.
I ran it at night and saw the coil wire on the passenger side had a small tear and was arc-ing.
Very hard to see during day and due to location.

Bulvot

Thank you, everyone. Lots of really useful advice and experience. It gives me a lot to not only check if the problem persists, but things to preemptively replace. It's all very helpful.

The new air filter arrives today. After I install it I'll provide an update.

dr bob

FWIW --

The debris on the MAF screen is definitive evidence that you have rodents dining on some critical parts. The filter media is easy to solve by adding intake screens as previously suggested. I've had regular black fiberglass window screen wrapped around the end of the funnels at the radiator sheet/fan console, secured with black electrical tape that's then hidden by the hoses. My original intent was to catch all the normal road debris that was making it to the air filter. Stuff like cigarette butts and some of the larger insects seemed to find homes on the filter media. Now that the car is more formally stored during the winter, the screens are undoubtedly helping with other things that would like to live in the intake area.

Rodents tend to do a lot more damage than chewing the air filter. They like to live under the intake too, and will munch on some very critical and expensive wiring while camping out there. For my stored car, I place mothballs in plastic bags at critical places around the car to make the living conditions a little more offensive to the rodent population. I punch a few holes in the bags so the scent can escape, and place them around the front and rear of the intake manifold, on the sides on top of the fuel rail covers, in the front area around the radiator, and on the sides of the engine trays where mice would start their journey up into the works. There's a bucket trap near the nose too, offering a fatal food source that hopefully is more attractive than the wiring in the car. There are some ultrasonic devices that help deter rodents and such, but K has said no because someone she knows thinks one drove their dogs nuts. She/we have cats, so that's out of the question apparently. I have the car up on stands for storage, although that just adds a few inches to how high the mice need to jump to get in a wheel and start their climb into the tasty areas.

There are several good threads on other methods folks have used to avoid the damage.

If you have an inspection camera (~~$25 tool/toy that links to your phone or tablet) you can look around under the intake for evidence of damage or nesting. That may influence your actions or at least the scheduling of the intake removal. Hopefully you've caught it in time, before major wiring damage has happened.

Wisconsin Joe

Just over the ends of the funnels at the radiator. It's nowhere near a concurs car, so I don't worry about looks. But I did give the screens a quick coat of black paint. And the basic design is that its sort of a 'cross shape.' The front of the funnel is covered (of course) but then it goes up the width of the funnel and out the height (the area that is beyond both the width and height is removed). Then the top, bottom & sides are bent in to go over the funnel. That holds it in place. I don't use any sort of fastener.

And a quick correction: I ran across a leftover piece of the hardware cloth. It's actually 1/2" squares. In reality, anything with openings small enough to keep mice out is good. I go with the idea that the smaller the opening, the more drag you are going to get. I don;t know how much more restrictive something like window screen would be over hardware cloth, but I like the 'less restrictive' stuff, even if most of the difference is only in my mind.

I've had issues with critters of some sort (most likely mice) chewing up the air filters on a motorcycle during winter storage. Where I am now, critters are less of an issue, but it's nice to be sure that the little buggers can't get in at any time (car sits a week at a time in summer).

Farris (OTR18Wheeler) made up some from some gutter topper. I saw those at the Dubuqe GTG a few years back.

Bulvot

My 928 seems to be running normally again. Cleaning out the air filter housing and replacing the air filter did the trick. I haven't taken it on a drive yet, and won't be able to for at least a few days, but it isn't acting at all like it was before.

I did inspect the valley and all wiring, hoses, and anything else that I could get eyes on . It all looked normal, no evidence of rodents.

Thanks to all of the advice and comments on this thread, I plan to have the MAF and LH rebuilt, do an intake refresh, and replace several other related parts and components. That work will have to wait for a few months, but it will definitely get done. Assuming that the car is, in fact, running normally again.

Thank you again to everyone who helped me sort this out and provided guidance on additional preventative maintenance.

To give some context on the condition of the car, motor and components. Not perfect, but pretty decent:

Bulvot

And thanks to the suggestions and idea on how to protect the air intake from another incursion. I'll put some thought into how I can fit something that would satisfy my sense of aesthetics.

Christopher Zach

See how things go. If you continue to have stumbling and issues you might want to look into replacing the ignition computers at the front of the car. They take the signals from the DME and switch the 12 volts to the coil, when they go wonky all sorts of insane timing hilarity can ensue.