TPS and AFR?

I noticed this Monday, that my car was down on power. I cleaned the MAF and it fixed this problem. After I cleaned the MAF, I tested the car and drove about 30 min's. While I was driving I logged my lambda, TPS and MAF sensor(s) with Durametric. It seem's that my car is running sligthly lean at WOT, Lowest lambda readings were about 0.97. That's about 14 in afr, and I would get better power from slightly richter mixture. Now, I have read that 70% max TPS signal is usual in these cars. Well that's the max I got. Will the ECU handle the 70% same as 100% or am I always on part throttle map??? My tra and fra values are with in specs. So should I get piggypack ecu and fine tune the mixture with that, or is there somethin else I should do?

Quotes source post: 10871307

Hard to imagine a MAF dirty enough to explain the down on power symptom. Did the dirt just run off the thing when you cleaned it? (Have to point out with a stock intake filter system and hundreds of thousands of miles I've never had a MAF get dirty enough to act up.) Chances are cleaning was uncalled for. More likely the MAF is acting up and the cool down the MAF got while being powered down/cleaned resurrected it. For a while. Under WOT the DME should go open loop and it can then fuel the engine to meet the torque demands of the driver as signaled by the gas pedal. The mixture should go richer, IIRC to around 13:1 as the engine makes max power at this mixture. During this WOT open loop mode the DME ignores the #2 O2 sensor readings, that is does not monitor converter performance as converter performance will fall off under WOT operation due to the richer mixture. This richer mixture time though is short lived. By my observation it takes a good deal of throttle, essentially the pedal needs to be floored, for the DME to enter open loop mode (from closed loop mode) and to remain there. An upshift can have this open loop mode continue but the pedal has to be mashed to the carpet again. Based on my info you are not operating at a part throttle map. If there is a pedal potentiometer problem the DME uses the lower voltage and limits throttle to 60%. Any acceleration is limited to 10%/second. As I started with I suspect the MAF is acting up. With a properly functioning MAF, etc, the AFR should be ok, though under closed loop mode a bit leaner then 13:1. The converters work best when fed the exhaust gases from an engine (a healthy engine) burning approx. a 14.7:1 A:F mixture. The converter efficiency drops off dramatically when the mixture varies from this 14.7:1 mixture.

Thank you Macster There was some visible goo on the maf, and I have encountered this same problem 2 years ago. Last time i changed new maf sensor. Before cleaning, car felt like it had 200hp, so the diffrece was huge. My car has cable throttle, so no pedal potentiometer. Throttle flap opens full, but the tps % is only 70. And only o2 sensors before cat.converters. So could it be, that becouse the ecu sees only 70% TPS signal, it will not go openloop at all? Car is slightly modified, but I think that stock ECU should keep up. Not sure thou, how far the stock injectors flow..

Quotes source post: 10871829

Wonder where the goo is coming from? Is the air box intact? Is the filter installed correctly? Are you using an aftermarket filter element? I have no experience/knowledge of the Porsche cable operated throttle. But if the throttle opens fully that's about as good as it gets. If the TPS is only 70% there may be a TPS problem and it is not signaling the throttle is fully open or open enough to trigger open loop mode. That could account for what you are seeing. You have to eliminate something being wrong before you question other things. There is the MAF. The TPS. The fuel supply. If the fuel pressure is not to spec the engine can run lean as the ECU expects a certain fuel pressure. If the fuel pressure is down the injectors will not deliver the expected amount of fuel in the time they are open. The ECU can increase the injector active time but there's an upper limit. Unless you have heavily mod'd the engine -- and you report you have only lightly mod'd the engine -- the stock ECU and injectors should be able to keep up. If you have the logging capability -- Durametric does this -- you can log the injector cycle time. I do not know what is the safe upper limit for the stock injectors though.

I think that the goo is from coolant residues. My waterpump started leaking 6 months ago on the highway. Before I noticed this, coolant mist was all over the engine bay. Including the airbox. I'll check the TPS first, if I can get it to 100%. Logging the injector duty cycle is good idea, will check that allso. I have tuned several turbo charged car's with standalone ecu's, and consider the 85-90% injector duty cycle to be max. Slightly modded in my case mean's ceramic coating in piston tops, ported cylinderheads, hevily modified stock muffler's. So I would say mildly modded.

Do you have an aftermarket air filter that uses oil for filtration?

Quotes source post: 10873956

Nope, stock airbox and stock airfilter.

Ok, problem solved. I adjusted the throttle cable and got the plate angle to 82%. (it seem's to be the max what you can get) There is no adjustment from the factory, so I cut the cable and used cable lock that I bought from motorcycle repair shop. Mayby not the best way to do this, but I think that the cable lock will hold. Connected the Durametric and took the car for a spin. It seem's that there is no rpm treshold for open-loop, ecu will monitor the tps signal only. Tested the car at slow speed with 6th gear and 1300rpm. On wot the ecu will go to open-loop. Not sure what % is the minimum, but 70% throtle plate angle isn't enough. The difference in power is noticeable thru out the rev. range. So might be worthwhile to check this, if you have cable throttle car.

My cable throttle is reading 70% at wide open and yes agreed it seems the 80ish % seems to be all you can get on inspection. I will try adjusting and see what happens. I too have noticed the car is down on power.