badass951

Long story short...my 951 runs perfect on part throttle and full throttle maps, but on idle maps it definitely runs poor (and it runs worse the hotter it gets - at first startup it hardly misses but at full operating temp it tends to miss more). Essentially with the TPS set off the idle contact (so that it is running on part throttle maps) and at the same RPM as normal idle (ex. 900 rpm) the engine pulls 17-18 in Hg and runs with an AFR of around 14.7 to 1. On the idle contact the engine pulls only 13-15 in Hg., runs around 15.5-16.0 AFR, and misses more (slight miss, or might I say skip, occurs still but not as frequently or as obvious). This is with the engine set at the same speed of 900 rpm and it runs drastically different. I am aware that the load put on the engine will be different with the fuel injection signal changing from idle to part throttle maps, but this does prove my engine is capable of running well at idle speed with the properly running engine electronics (which should help narrow down the cause).

Anyway, the car has a rebuilt engine with modifications including lightened crankshaft, lightened flywheel, custom turbo, siemens 55# injectors, Vitesse MAF + chip, raceware head studs, manual boost controller, turbonetics 42mm racegate wastegate and the list goes on (although nothing that should affect idle).

As far as parts replaced the following list has been replaced:

- ISV (was leaking air)
- vac. lines
- ignition wires (8mm paragon) and plugs (NGKBPR7ES)
- EVAP control valve (not the brass one, the black and white plastic one - forget if it is control valve I or II)
- DME (replaced with rebuilt DME)
- wiring harness has been replaced with another that was repaired to 0.2 ohms or less across every wire

Anyway, the TPS passes all tests on clarks-grage.com and is clean inside (only unclear thing I saw in the tps was the ends of the burshes where they contacted the potentiometer seemed oily or greasy maybe? but my eyes can't see enough detail to know if this is the case or the ends of the brushes are just black). I still feel as though the TPS is a suspect, as clarks-garage states that TPS problems can occur when hot, although I am not sure the idle switch would really be affected by heat?

Another interesting note is that when I bridge the port to disable the ISV it seems nothing happens (or at least that I can detect). The wiring to the port terminals has been checked and there are no detectable shorts or high resistance using a multimeter. I am confident the wiring is ok, but worth noting.

Confirmed by another post I made today, I am running without an O2 sensor and essentially from my knowledge about the operation and self-generating voltage that an O2 sensor creates the signal that my DME should be seeing is lean and therefore would cause it to richen the mixture. Also, I run a PLX R-500 and have used the narrowband output to the DME and have also had it disconnected and either way it runs the same.

I have smoke tested/pressure tested and can find no current leaks. Unless it is something silly like the pressure sensor in the KLR leaking and then not leaking the smoke out through the KLR itself, I do not think I have any vac. leaks. It may be worth noting that when smoke testing the only time I saw smoke was under pressure and the smallest bit came from oil filler cap seal, although the oil filler cap was purchased within the past year and the seal looks fine. The only reason I am even saying this is that I regularly find lean idle conditions on Audi vehicles when there is an internal leak within the crankcase breather system - just not sure where this could even happen in our system though (especially because I have done the venturi delete and simplified the system).

So, I am out of ideas on what else to say about this problem, but I will continue to update with any essential info. To repeat though, the problem I am trying to solve is a slightly lean idle, with a slight miss/skip with the engine only pulling 13-15 in HG. Thanks in advance!!!!!

Ski

here is an interesting TPS site also, not sure if Clarks has a reference to it but maybe it will help.

http://www.arnnworx.com/tps-repair.htm

If you unplug the TPS with your engine running, what happens to the revs?

Jeremy Himsel

Just a thought for you, but I had a similar issue with 55lb Siemens Injectors. It ran fine at part and full throttle (but lacked some power that I didn't notice). At idle it ran pretty rough (missed) unless I richened it up quite a bit with my AFPR 13.0 - 12.8. After replacing every sensor on the car, I swapped out injectors with another new set and the problem went away.

I then sent them out for flow/cleaning and they checked out perfect. I installed them again and the problem came right back. I finally started swapping out one at a time until I found the bad one and replaced it. I sent it out to get checked and they said it was perfect. These acted this way right out of the box.

When I upgraded injectors again I sold the extra new set I had to Dan (XSboost). First I had them flowed and cleaned even though they had very little use. They checked out perfect but when he installed them his car ran terrible because of a bad injector. I sent him a new one and all was well again for him.

I chased this issue for a year and threw up my hands quite a few times because everything checked out fine and these were bought new and I tried every test on them I knew (spray pattern, flow,firing, cleaning). You may just have one injector that is not operating properly @ the idle speed fire cycle and causing the entire AFR to go lean. If you richen the car up does it smooth out? I'm assuming you have a fixed 3.0 bar FPR but if you remove Vacuum from it does it get richer and slightly smoother? You may try and clamp the return line a bit to raise fuel pressure and see if it gets better.

Jeremy Himsel

BTW, @ start-up you're getting cold start enrichment for the first minute or two so that's probably why it runs better. Send me a PM if you want to chat about it.

Ski

944 chat, hell does anyone use it?

Jeremy Himsel

LOl, hell no, I was going to give him my phone number. I type too slow.....

badass951

Check your PM. My car definitely runs better at idle on the +10% fuel map of the Vitesse chip. Not perfect, but slightly better.

badass951

Today I tried unplugging the TPS and then running the car (did not unplug while it was running though) and noticed it started up smoother and went right to 900 rpm. It also pulled 17-18 in Hg and ran in the 14s AFR, but I guess it is running off part throttle maps as I tested before. Normally it starts at around 600 rpm or so just for a short bit until it is going anywhere from 900 to 1100 rpm. It stays smooth, just changes depending upon temp or sometimes even after a throttle blip.

EDIT: was smoother with it unplugged and in the 14s AFR, but still had a slight miss just even less noticeable

Bri Bro

What size injectors and what is a AFR at idle? Sounds like a problem I had, ran better on the AFQ third setting.

badass951

55 lb/hr siemens. AFR at idle is near 16.0. And yes it does run better on the third setting. Your problem was injectors?

A.Wayne

My .02
The injectors tested fine because nothing where wrong with them.
The AFR numbers he is trying to achieve is possibly too lean for the type of injector /driver combination. The missing you are experiencing is from the injector spotting due to the lean AFR and your injector driver inability to control the injector at that duty cycle. Run at a slightly richer AFR and this will go away or change injector type to say Delphi .... what's the impedance vs stock and are you running inline resistors ?

Bri Bro

Same setup, same problem. Never did get it to run right. Went to another MAF setup after I tired everything and needed to get the car running.

hally

I had a strange problem with my Delphi 55 injectors after the car was sitting for 12 months and pulling / reinstalling the engine. They were not firing, so cycled through starting the car with only one injector connected at a time which woke them up. I was then still getting some misses with all four connected together until I reduced the resistor ohms from 1.5 to 1 ohm.

brad-cam

Wow, here's a thread I've been waiting for. I have a similar setup (Vitesse MAF, 55 lb Siemens injectors) and have a similar symptom. It runs a little rough on idle, rougher than it should, smooths out off-idle and the TPS is new. The AFR though according to the LC-1 wideband at idle is where it needs to be around 14.5-14.9 but fluctuates and gives a little stumble. Idle vacuum in 16-17 inHg. Coasting vacuum is 22 inHg. I'm pretty sure I don't have any more vacuum leaks, have replaced the ICV and have venturi delete. I've learned to live with this, but maybe it is a bad injector. I'll try richening it a bit using the SMT6 and see if it helps.

Jeremy Himsel

He's running Siemens 55lb injectors (3102's) which is the "popular" injectors for these cars. They have no problem running in a 951 at the idle duty cycle when operating properly. In my case the injectors tested fine in all respects but when I replaced one of them all the problems went away. Pretty simple to say the injector was was not functioning properly. This happened on a second set that I sold to Dan Jaunch and replacing one injector resolved the problem (although his was much worse).

Prior to swapping the injectors one at a time I tried 2 DME chips (sorry John), 2 MAF's, 2 DME's, 2 02 sensors, and replaced the knock and DME temp sensors to no avail.

His symptoms and mine are virtually identical and once I replaced the bad injector I idle @ 14.7 - 14.8 @ 3.0 bar of fuel pressure with the Vitesse software and FQS at the factory settings. Oh yeah my SMT-6 is completely zeroed out.