awilli6

Hey Gang,

My 89 S4 just doesn't seem to be running as strongly as I remember my 87 running. I recently put in a rebuilt MAF and LH after intermittent "shut offs" and no restart issues. I've driven it a several times since then without those issues. It just doesn't seem to have the same throaty "Vroom" that it should have. When I burp the throttle hard while idling, the exhaust seems to cough at the top of the rev. (Vroom, slight cough)

Also when I'm driving and hit it hard (WOT), it doesn't seem to be a health, throaty sound. HARD TO EXPLAIN. Maybe the timing is being retarded?

I changed the plugs about a month ago (NGK). I changed the two coolant hoses that run under the cowl next to the wiper motor and I've done a ton of work on the car overall since 2017 (MM, TB/WP, Steering Rack, Shock all around, rear axle boots, OPG, AC actuators throughout, replaced fans, etc.

My Question: Is there something I can check to see if the timing is being retarded? How would I know if its running lean? Would that cause issues like I describe? Or do you guys have any suggestions on things to look at? Prior to the MAF and LH, I can't remember the type of response I get now.

i know this is not very clear but I can't upload a video of the idle for some reason.

Ash

Wolfman928

My 1988 was a bit sluggish until I replaced the Hall sensor and knock sensors and some others electrical connectors around the engine, it's some stuff neglegted over the years. I know the timing can go off because of broken cam/knock sensors.

cheers

FredR

If you do not have any means of interrogating the system disconnect one of the knock sensors and see if it makes any difference. If it does then the problem is not the knock sensors or the Hall trigger, If it makes no difference then one of those items is down. Failure of just one of those three items pulls the timing back 6 degrees across the board and that is significant.

Mrmerlin

post a picture of the engine when was the last intake refresh done
when did it stop working as it did
IOW what was the last thing you touched

dr bob

The '89 has pretty good diagnostics in the controllers, so an early step would be to find/borrow/connect a diagnostic tool to the connector next to the passenger seat and see what the controllers report. There are several options for those diagnostic devices. Your sensor-failure options that affect timing include the Hall sensor that sits behind the right (passenger on US cars) side of the engine just behind the cam gear. Also included, either of the knock sensors under the intake. Hence the suggestion from Fred that you selectively disconnect each one and see if performance drops. If performance stays the same, than it can still be any or all of those sensors. These sensors are typically replaced as part of an intake refresh exercise, hence Stan's question about if or when that was last done. The Hall sensor connection is on a hang-on bracket on the engine lift eye at the front of the right side cam cover. The rear knock sensor terminates in a bracket on the right side fuel rail. The front knock sensor connector is at the front of the intake above the water bridge, near the flappy solenoid. If you have one of those handy endoscope/bore-scope inspection cameras, snake the camera end under the intake and look hard at the cables that connect to the knock sensors. Oil under the intake takes its toll on those cables, as does carburetor or brake cleaner too often used to try and clean the valley they live in. Cam cover and oil filler neck leaks, crankcase vent hose leaks, etc all contribute too damage to the knock sensor wiring over time. Heat there doesn't help either. It is possible to replace the knock sensors without lifting the intake if you have small hands and don't mind sharing blood with the engine. You'll want to replace a lot more stuff under there though, making a full intake refresh the easier way in the end.

One other thing that falls off the radar is the oxygen sensor. These have a service life of maybe 50k under good circumstances. That sensor is key to "teaching" the LH controller about the MAF calibration ongoing, so a deteriorating oxy sensor can easily negate some of the benefits of the rebuilt MAF. Good News is that the oxy sensors aren't expensive, and are relatively easy to change while the car is up for something else. Penetrating fluid on the exhaust flange studs and maybe spare gaskets will make lowering the catalyst section for the sensor change a bit less work. Should be on everyone's maintenance schedule really.

awilli6

Thank you for all of the suggestions guys. I’ll check the sensors later today. I haven’t done an intake refresh. The hoses and sensor wires look new. I did have to add clamps to hoses the PO left off. I do plan on intake refresh in near future. I’ll call Roger for the O2 sensor.

Shark2626

The correct spark plugs and gap may be worth looking at. Bosch Heavy Duty or the equivalent Bosch Super Plus, its listed in your owners manual.

Bill Ball

Make sure it is running on all 8 cylinders. These cars run pretty well on 7 or even 6. Anyway, look for dead cylinder by pulling spark plug cable caps one at a time while the engine is idling. Each time you pull a cap, the engine SHOULD run a little rougher. If you pull a cap and there is no change, you have found a dead cylinder. The cause could be spark or fuel related. Could be a bad spark plug, spark plug cable, or injector. Just a thought if the aforementioned diagnostics don't show anything.

awilli6

Thanks. I’ll take a look at that. I did replace the plugs recently.

Petza914

Maybe you didn't get one of the plug wires securely connected.

awilli6

Hey Guys,

i unplugged both knock sensors and hall sensor once at a time. There was no change in the idle. Is it strange for all to go at once? Is there a relay that controls these? The sensors look new. I haven’t done an intake refresh but the PO May have because they really look new. There is no oil under the intake. I’ll try and take pics under it and post.

Dr. Bob,

i don’t think my hand are small enough to fit under the intake. If possible, would I go in where the MAF is? From the back side?

Speedtoys

It can also be a bad Hall sensor too that just like -1- bad KS, will retard timing 6d at all times.

One of those three is bad.

Look for the HS connector by/near/at the pass side timing gear cover down the side of the engine. Looks just like the KS plug.

awilli6

I unplugged the hall sensor also. Neither changed the idle.

Speedtoys

Then Id be willing to bet one of the three is bad.

Canvass for a diag tester to find out which one, or find someone with a Sharktuner to swap ECUs with to read which one is bad.

Shark2626

It sounds to me to be a combustion under heavier throttle issue that you are noticing, as you have described it. Which would steer me toward the plugs (that you just replaced and then noticed the issue), the wires, or the fuel (octane). IIRC you tend to favor newer / exotic style parts for your 1989 car, ceramic fuses for example. Some NGK plugs that fit this car can be quite exotic and very modern but may not provide as good of an experience as the Bosch plugs that are recommended by Porsche, but then again some versions might. Which NGK plug did you go for?