Emissions analysis assistance

Moneyguy1 · 06-05-2003, 11:38 AM

OK, Guys,, first the good news. With an accepted value of 220 parts per million, our Passat (after I tuned it up) passed with a reading of 4. Outstanding!!!

Now for the 1984 944. Last year, I installed an new O2 sensor and knocked that down form a loaded reading of .53% to .14% (1.2% permitted). Now I would like to attack the HC part of the problem. The "load" test shows 92 ppm with the 220 permitted. However, the idle shows 201ppm which makes me uncomfortable.

What should I be looking for? I hesitate to remove the throttle body to check that switch unless it is a real probability that is where the problem is. That would require having a new gasket handy. The air flow reads within the limits posted in the Haynes manual; the car has recent upgrades to the ignition wires and starts on the first twist of the key, although it runs roughly for the first minute or two.

I will appreciate any suggestions from the gurus out there

Thanks in advance

Bob S. Tucson AZ

MrPants · 06-05-2003, 12:15 PM

czn you be more specific as to what "running roughly" means? also have you noticed when exactly it stops running rough? at a certain temp?

Moneyguy1 · 06-05-2003, 12:23 PM

Not even off the peg when it starts running properly. Can't give you a more specific answer, unless I added a much more accurate temp display. Going only by the dial in the instrument cluster

Scott R · Scott R's Garage

Something easy that you can try is to take the throttle body off and clean it up, you may have some blockage internally.

Also I know that you checked the voltage on the AFM, but how is the spring action? The condition you described reminds of when my AFM was on it's way out. The spring was weak and it had symptoms not unlike the ones you're describing.

Moneyguy1 · 06-05-2003, 12:36 PM

Thanks guys...Keep the recommendations coming!!

Looks like I will wind up removing the throttle body anyway just as Scott says to "clean it up".

Scott..is that spring independently replacable?

AFJuvat · 06-05-2003, 12:50 PM

Not listed as an individually listed replacement part.

Sould suggest making sure the idle is set properly (840 +-40) and that the engine is getting enough air at idle.

Check the intake boot for hidden cracks (usually the underside)

Get a few cans of brake cleaner - it can be burned by the engine and it dosen't leave a residue.

Throttle Body: brake cleaner in the throttle body You don't need to remove it to clean it out. Keep the butterfly closed and spray it down - after that is cleaned up, spray out\wipe up the inside.

You can soak a rag in the stuff and clean up the area where the butterfly seats in the throttle.

If you are feeling brave, remove the idle adjust screw and spray out the air bypass passages - otherwise, just spray out the passages the best you can with the screw in place.

After a good cleaning, you will have to reset your idle

AFJuvat

Moneyguy1 · 06-05-2003, 01:12 PM

AF: Good info. THe boots have been removed and flexed, looking for cracks, seem to be excellent. I am under the hood on a regular basis. But in order to check the throttle switch, will I not have to remove the TB itself?

Thanks!!

AFJuvat · 06-05-2003, 01:19 PM

To check general function, no, you can also make small (emphasis on small) adjustments right at the throttle body rather than moving the switch. That odd looking screw that is secured by a nut is used to make small adjustments - the object is to get the throttle switch to "click" right as the throttle cam starts to move.

If you are flexable enough and can work by "feel" you can remove the switch without removing the throttle body. ALternately, you can go at it from the bottom if you can get enough clearance.

AFJuvat

Kirby2 · 01:30 PM

Two questions:

How old is the Catalytic Converter?
If it is OE, spend the $200 and get some increased performance to boot. (Any good muftler shop can do it in an hour for $200 out the door).

How long since you have had head work?
Worn or cracked valve seals will allow oil to effect idle running, but is diluted out with the higher RPMs.

(Leaky Fuel Injectors will also give you higher Idle HC.

Moneyguy1 · 06-05-2003, 02:42 PM

Cat is about 4 yrs old. Engine uses no oil between changes (no obvious gas smell on the dipstick), and has slightly less than 70k on it verified. As far as I know, never had the head off; no leakage problems. Once the engine gets through its initial minute or less of stumbling, it runs strong with a rock solid idle of 850, and this should eliminate the cause of the problem as vacuum leaks, although I am about to change over all the vacuum lines simply to head off any potential problems. I have checked the output of the injectors and they fall into the nominal output with a good spray pattern. Fuel filter is new, the fuel pump appears to have been changed at some point, but there is no record of that in the POs records. Front end totally resealed exactly two yrs ago with all recommended parts replaced.

Very good throttle response from a standstill. Heck, if it were not for the relativly high HC reading, I would leave it alone. When I say starts with the first twist, I mean even after sitting a week or so. No cranking. Just fires over. With the Passat, I had a "hard starting" problem. Turned out to be a bad injector that depressurized the system by leaking. Replaced that and eliminated the problem.