nize

so after i installed the air-fuel gauge, i've noticed that under normal driving, while cruising on the freeway at a set speed the a/f ratio will quickly alternate between rich/lean as per normal.

if i let off on the gas and coast and let the engine brake, the a/f ratio will go beyond lean, because the injectors shut off. once the rpm drops to around 1200, the injectors will turn on again to prevent the engine from dying and the car will idle. during idle, the a/f ratio will alternate between rich/lean as per normal.

now the odd part;
while cruising on the freeway, sometimes if i let off on the gas and coast and let the engine brake, the a/f ratio first goes beyond lean as normal, but then i notice the a/f ratio 'blipping' to rich about twice per second. it almost seems like one (or more) of the injectors are not shutting off when they should, or they're sporadically turning on. has anyone heard/seen anything like this? does anyone have any idea what might be going on here?

oh also, each time the a/f blips to rich, you can hear sort of a backfiring sound in the exhaust. the whole time i'm not giving any gas and the car is engine braking.

thanks.

edit: note that the 'blipping' problem is not the same behavior encountered during normal cruising where the a/f gauge constantly jumps between rich/lean. when it's blipping, it's usually beyond lean, and then will 'blip' to rich and shut off, and repeat every half second or so.

Tom M'Guinn

The DME shuts off the fuel when the TPS idle contact switch is closed over 1600 rpm or so. My first guess for your issue is that the TPS idle switch is not staying closed when you let off the gas. Any chance it is old and/or that it is clicking open momentarily as the car bounces down the road?

Chris White

I second Tom's suggetion. Either the TPS or the wiring to it.

Chris White

Porsche-O-Phile

Check for a blink code (IIRC it's #41) for "TPS disconnected" or something like that. It does kind of sound like it might be something related to the TPS. . .

nize

okay i've removed the tps, i don't hear a 'click' when i turn the dial so that means it doesn't know when the throttle has been closed.

is there any way to repair this? the plastic case seems to be pretty well glued shut so i'm guessing not. and a new one seems to be over $100. anyone got a good working used one they can sell me for cheap?

awilson40

Its really not worth buying a used one. My old one would check perfect but still throw KLR fault codes.
I installed a new one and no problems for 2 years.
If you shop around I'm sure you can get it cheaper.

nize

btw, does anyone know which of the 6 pin connectors do what on the TPS? they seem to be numbered in reverse from the front: 6-5-4-3-2-1

edit:
porsche part number is:
951-606-113-00

bosch part number is:
0-280-120-400

awilson40

here ya go

nize

okay i've done a bit of research on this, and i've gotten hold of a brand-new tps. it turns out that the 951 tps doesn't 'click' and never should. the reason is because it's a straight rheostat, so there's no reason for it to 'click'.

the n/a 944 tps however, does 'click'. the n/a 944 tps is basically an on/off switch so it makes that 'click' sound when going on/off throttle.

i think people who have the troubleshooting write-up for the 951 tps should correct this, as none of the 951 tps should ever make a 'click' sound.

the only way to check proper operation of the 951 tps is to check the various resistances with a multimeter.

i'll pull the old one today and let you know how it goes.

Tom M'Guinn

Nize,

Where are you getting your information? The turbo TPS has two circuits -- an idle contact switch (that clicks) and a throttle position sensor (potentiometer/rheostat). I just confirmed on my own car -- it clicks!

nize

i'm getting my information from britwrench, at gerber motor sports (porsche specialist shop). and i also have a brand-new stock bosch tps for a 951 here right out of the box, it does NOT click.

perhaps the click sound you are hearing is from the metal throttle cam hitting the stop? hmm.

shaheed

uh no...the tps IS supposed to click, here is some information on the lindsey site about how to adjust your tps here

Bri Bro

Nize, trust me, it clicks. I have worked on several of them. The click is the switch closing telling the DME you are at idle. You have to adjust it to get the click, maybe you need to install it, then adjust it and see for yourself. It is a very easy job, two screws and a connector.

BTW, I needed to replace one over a weekend. I went to Autozone and they did not have a listing under my year/model. I gave them the part, he did a search on the number on the part and came back with a exact match. Worked great.

nize

okay i've installed the new one and it's solved all of my problems. no more random rough idle either.

the new part is installed and it still does not click. however, it appears to be working just fine. i'm tempted to go to the dealer to have a look at the part to see if it really does click.

beab951; how much did the tps cost you from autozone?

shaheed

if it's not clicking it's not adjusted properly.