_Thomas_

Hi

1984 928 S2 Euro (310 hp) idles nicely, runs/accelerates very well at WOT and above 2000 rpm, but annoyingly hesitates/staggers a bit around 1500 rpm, especially when accelerating lightly (this is quite nocticeable e.g. going away from a traffic light, not being in a hurry).

I have done electrical and vacuum tests as good as I could, but I still may not have found all vacuum leaks or faulty electrical (ground) connections, but planning to do it as seriously as possible next occasion, I might have to buy (take home from work ;-) ) a vacuum tester/good multimeter.

I have asked this question already on the German message board, and people are really helpful, I got a number of responses, but as I understand it is quite a tricky problem which can have different (or several) reasons, also from searches in the archive I have found quite complicated cases which have obviously gone on for years and sometimes there was no final conclusion. Before I start buying new ignition wires etc. I am just hoping somebody recognises the problem which I am sure must have a very simple solution.

Cheers Thomas

Drewster67

Hello Thomas -

This is what I would do -

Not in any particular order.

1. Verify Battery Amps and Voltage
2. Clean/Replace Cap and Rotors
3. Test/Replace Spark Plug Wires, verify they are seated correctly.
4. Clean/Replace Spark Plugs (ensure gap is correct)
5. Ensure 6 Pin Connector is seated onto MAF
6. Clean Fuel Lines (system) out
7. Inspect/Replace Fuel Filter
8. Ensure 13 mm Bolt on Distributor is Tight
9. Ensure the two pin connector is seated onto lower air box.
10. Ensure TDC Sensor is seated properly as well as the other one (Sorry - having a mind warp (forgot it's name) but it's seated atop of the engine - directly under the firewall - both are adjacent to each other)
11. Verify timing is set at TDC at all three points - Right/Left Sprocket and Camshaft.
12. Verify alternator is producing required voltage and the belt is tight.
13. Switch to a different brand of Petrol using the best 91 Octane possible.

Just a short Brainstorm on my part - Hopefully something listed will correct your issue.

Good Luck

_Thomas_

Thanks Drew

1. Verify Battery Amps and Voltage
Battery is new, 88 Amps, also I cleaned all connections there and pretty much elsewhere (according to Wally's checklist)

2. Clean/Replace Cap and Rotors
I had a look inside, they seem all right, but of course I can still buy new, but want to avoid at the moment, this is why I post again

3. Test/Replace Spark Plug Wires, verify they are seated correctly.
still have to measure their resistance, but they are seated all right and have no cracks

4. Clean/Replace Spark Plugs (ensure gap is correct)
they look quite new, colour of electrodes normal brown

5. Ensure 6 Pin Connector is seated onto MAF
is okay, have even cleaned it with contact spray

6. Clean Fuel Lines (system) out
I put 1/2 liter of STP fuel system cleaner in last gas tank, and injection system cleaner in the one before

7. Inspect/Replace Fuel Filter
this i haven't done yet

8. Ensure 13 mm Bolt on Distributor is Tight
I am not sure what you mean with that right now, but I will try to find out when I am there.

9. Ensure the two pin connector is seated onto lower air box.
It is there.

10. Ensure TDC Sensor is seated properly as well as the other one (Sorry - having a mind warp (forgot it's name) but it's seated atop of the engine - directly under the firewall - both are adjacent to each other)
Have to check that.

11. Verify timing is set at TDC at all three points - Right/Left Sprocket and Camshaft.
This will leave to the mechanic when I will have the timing belt tension checked (just replaced the timing belt a couple of days ago)

12. Verify alternator is producing required voltage and the belt is tight.
All belts are new (fitted together with timing belt last week). Voltage I still have to check with proper voltmeter.

13. Switch to a different brand of Petrol using the best 91 Octane possible.
I am using 98 octane all the time (super unleaded as we call it) :-)

Best regards
Thomas

Bruce Sinclair

Another place to check is the grounds (2) on the right cam cover, These ground the fuel injectors and the brain. This problem had me going nuts on my car, mine were loose. It showed up as a miss at 2000 rpms and progressively got worse.

Old & New

Sounds like a lean condition.

Drewster67

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Bruce Sinclair:
<strong>Another place to check is the grounds (2) on the right cam cover, These ground the fuel injectors and the brain. This problem had me going nuts on my car, mine were loose. It showed up as a miss at 2000 rpms and progressively got worse.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Bruce speaking of grounds -

What color are your grounds?. Reason I ask is because I have two brown wires ground to the cam tower then one black wire going to the a/c compressor then another black wire hanging freely?. I'm trying to trace the free wire -

Thomas - The 13 MM bolt is the bolt that secures the dual distributor in place -

Also, Not all Brands of Fuel are equal - Some are better tha others - Just because the octane rating is the same doesn't mean the quality is. If they have Chevron across the pond, that would be my first choice.

TIA

reno928s

Thomas, I have the exact same problem with my 1984 928S Euro. So far I have changed the spark plugs, SP wires, cap & rotor, and fuel filter. I can't recall but someone said it might be the alternator. I'am going install a new fuel pump, temp sensor, and have all my injectors cleaned and blueprinted. Hopefully by next weekend. And if that doesn't work I'll just post it everyday on Rennlist. Sal

Normy

OK...

So now I don't feel so left out!

See my "Rough Running" threads on this one. I have an '85 S2 5 speed, and have been all THROUGH that engine trying to figure out why I get a miss under high throttle conditions.

Symptoms: Under hard acceleration, the car misses, seeming to run on 7 cylinders for a few seconds as the tach winds out. Suddenly, and at no particular RPM, the miss disappears and the car rockets forward.

So far, I have basically replaced the whole ignition system save the EZK brain and the transistor units near the hood latch. I have checked all the sensors with a multimeter as per the manuals [checks out perfectly], took the car to Zotz Garage in Winter Park [specialist in Porsche's, and the owner races...] and had a suitcase-mounted diagnostic tool hooked up [no problems could be found], and recently....I had the injectors professionally cleaned/rebuilt by Rich at Cruzinperformance. All to no avail- I'm glad my trip to Sharks In The Mountains did not involve any racing or anything....I'd have been quite embarrassed!

-I've poured literally gallons of Berryman B12 fuel injector cleaner into the tank, and even jacked up the front as high as I could get it...and carefully drained as much of the fuel out of the tank as I could, then flushed it with good gas. I did this because the exhaust has a funny smell at times- like its getting bad gas or that brake fluid is somehow being drawn in. The later is not likely, as my brake fluid level stays pretty constant. Still not running right-

Yes, I've cleaned all the grounds, and even replaced the seal between the MAF sensor and the elbow, something that hasn't been mentioned in this thread yet. When I had the injectors out, I noticed that the elbow/throttle body was not secured to the block- the three studs apparently have been broken off or the whole assembly is out of whack somehow, and that the clamp holding the whole thing to the spider was loose. Tightened all that up, and when I had the engine running, I used an un-lit propane torch to find intake air leaks. Everything seems pretty tight now.

It seems to disappear on cool nights- whooo eee! Fun-land, and the tires hate me. I've also noticed that changing gas constantly seems to help- for years I ran only Chevron, but lately I don't take the same brand twice and that causes it to run noticeably better for a while.

After the fuel injectors were rebuilt, I was amazed how much smoother the car ran. I have never had any odd idle problems as are commonly described in this web forum, but the rebuilt units went in, the car seemed to stall at stoplights...only, it wasn't stalled- it just ran that much smoother! Rich found that two injectors were leaking after shutdown, and that there was a 17 percent difference in flow between the "richest" and the "leanest" of my injectors! Two of them were not salvageable, so I have 6 rebuilts and 2 new units installed. Total cost, due to the two new ones [rare: the Bosch part number is 028 150 252 for S2's] was over $325....yuck! But now something interesting is happening. I'm not certain if I did it by rerouting the idle stabilizer hose around the outside of the air box support instead of inside [it looked kinked], but now when I start the car, it idles at different speeds on different days. Sometimes around 1000 rpm, other times around 500 and it wants to stall at lights. The whole time...it idles smoothly.

ARRGGHHH!

Well, I must have a bad wire somewhere- eventually I'll figure all this out!

Normy!
'85 S2 5 Speed

Normy

Another thing to add...I've tested personally, and had tested professionally the MAF sensor on my car. And I've adjusted it from time to time as well, via a 3 mm allen wrench. I've noticed that the adjustment screw does not seem very tight at all- much looser than I would expect. Has anyone ever adjusted this? Just how tight should that adjustment pot be?

And is there a shop that rebuilds MAF sensors?

N!
'85 S2 5 Speed

Reinhardt

On my S2 it turned out to be the throttle position switch that caused the exact symptoms you described. Check it out.

_Thomas_

Hi
@Bruce: will check them, thanks
@Old&New: I agree, just not sure where it is coming from (vacuum leak or not enough fuel or maybe fuel jets)
@Normy: actually I read your story before :-) misses at WOT sound even more frightening

@Reinhardt: sounds very interesting!! Please explain more! from what I read the throttle position switch tells the computer when the accelerator pedal is not depressed (idle, overrun) and when it is open more than 30 degrees (WOT, no problem there).
So what is the throttle position signal between 0 and 30 degrees of opening?? is there some potentiostat, are there any resistances I could check?

Cheers Thomas

Niels Jørgensen

You can add me to the list. My problem usually goes away after I fiddle with something, making me believe again and again (ok, so I'm naive) that I've found and fixed the problem. So far, it has always returned - sometimes in a few days some times after several weeks.

Also, it is never a constant problem.

As far as plugs, cables, rotors and injector cleaner/different fuel goes, I've BTDT. I've also done the basic checks on the MAF and found no faults.

If I don't find this problem soon I'm going to get a new license plate that says "GRUMPY!"

Old & New

Normy,

High output miss that goes away on cool nights? Sounds like an electrical fault. Swap out those two ignition parts that you have been saving for last. ;-)

Drewster67

This is reaching for us U.S. Boys - When the cats get old, the tend to break up. When it breaks up - little peices of honeycomb can clogg the exhaust pipes restricting the exhaust flow. Which in turns can cause a miss and lack of acceleration.

Thomas - the other sensor that I forgot it's name, is the throttle position sensor.

Make sure the MAF is seated onto the throttle body squarely.

Drewster67

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Normy:
<strong>Another thing to add...I've tested personally, and had tested professionally the MAF sensor on my car. And I've adjusted it from time to time as well, via a 3 mm allen wrench. I've noticed that the adjustment screw does not seem very tight at all- much looser than I would expect. Has anyone ever adjusted this? Just how tight should that adjustment pot be?

And is there a shop that rebuilds MAF sensors?

N!
'85 S2 5 Speed</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">On mine, it's pretty tight. The funny thing was, when I first got my shark, it had an aftermarket potionmeter (Sp) spliced into the car by the fuse box <img src="http://boards.rennlist.com/upload/0603_001.jpg" alt=" - " />

I have no idea if this aftermarket device was used to pass federalization but I removed it and rewired the wires back to OEM. To me, there is no difference in performance.