dougn

my car has lethargic throttle response and always has. when it's dead cold right after start up, it's very snappy but quickly loses its response as it starts to warm up. after about a minute or two it feels like there's a time delay between a small stab of the throttle and the reaction.

so i'm thinking it is the head temp sendor's input that is causing the computer to lean the mixture and cause the slow response. so....

i wonder if the temp sendor is not working properly or ....maybe i can alter the resistance value to cause the car to run a little richer under part throttle conditions????

BTW i've tried a host of other things to try and remedy this but none have had any effect

Heirsh

Not that I am advocaying running w/o it at all, have you tried running w/o the o2 sensor? my car runs better w/o it in hot weather, though I don't run like this normally.

also if you have an early car you can richen it with that switch. Though with the ox sensor connected richening mine just gives poorer performance.

Just a cpl thoughts

dougn

yup i tried it, didn't help. i don't think i have a switch. what is that switch for again?....low fuel quality?

Heirsh

it adjusts timing and fuel. there are a cpl threads about this recently. I think it is only on '90 cars.

Good luck with your problem!

garrett376

In the first minute or two of starting a cold engine, the O2 sensor is ignored. As the sensor warms up, the engine starts using it. You might be looking at a bad O2 sensor. Best way is to monitor its voltage output while driving using a Bosch tester to see if it's out of spec. How old is your sensor? Any record of replacement? The O2 sensor would be a potential source, as could a cylinder head temp sensor. The Bosch Tester can tell you the "health" of each of these.

dougn

it's a new o2 sensor and it didn't help.

have you ever seen a bad temp sendor?

springer3

There is some chance you have debris around the cylinder head cooling fins, and the DME is protecting the engine from high cylinder head temperature. If you have a bad sensor, your DME is in safe mode.

Check the fault codes, and replace the bad component. If the cooling system is clogged or dirty, fix that. Don't try to fool the DME with dummy resistors. It is too easy to find and fix the real problem and keep it working as designed.

dougn

no everything is spotless. i had the engine out recently and did a seal-up and thorough clean up.

i don't get any fault codes using the gas pedal method

chancecasey

I've got the pc-based diag software and interface if you want to try using those.

dougn

i'm not familiar with it. what does it tell you?

chancecasey

The Scantool one, you know...

https://rennlist.com/forums/showthre...ferrerid=35219

dougn

wow that's amazing. i didn't read that thread....

frankvan

Dougn,
any updates on your throttle response quest?
I just got my 91 Alfa back on the road (second car in the avatar) which is also a Motronic controlled engine (except water cooled) and its throttle response is like a sport bike compared to the Porsche. I'm curious as to what can be done to improve the P-car engine so that its as quick.

dougn

i have posed this question time and again but i haven't found a problem or figured out how to improve the response. my 91 BMW that uses motronic has a very snappy response too.... so i know it can be done

seems like it needs a larger shot of fuel because it is very responsive when cold

i can't even find anyone who seems knowlegeable about the fuel pressure regulator.....it may be the key to the slow response.

the regulator has a vacuum line connected to it that reduces the fuel pressure to about 50 psi while under vacuum. when vacuum is removed, the pressure increases to about 55 or 58 psi. when you open the throttle quickly, vacuum goes away ....so i'm concluding this increase in fuel pressure is designed to provide throttle response.

JasonAndreas

The ECU also adjusts acceleration enrichment in response to how quickly the AFM voltage changes. And that amount is reduced as the CHT increases. Is it possible your AFM is getting laggy? You could always try Porsche's fix and add a TPS.