My idle is between 10.6-11 on the wideband. It idles a little rough but drives fine, it just doesn't seem to "like" where its idling. Sometimes it shakes when the idle gets low. I've been using the idle adjust screw on the TB, but its almost all the way in (can't really raise idle any higher) and it still idles around 700rpm. When warm it catches at 1200rpm then when put in 1st it drops beck to 700rpm. I don't have a BAC, could adding one help any at idle? What can manipulate mixture (so to speak) on an s5?

90 vert
stock t2 block, stock turbo
550s, 720 sec with Rtek 1.7
RB older style full T2 exhaust
no emissions, no bac
throttle body mod
FMIC
*Starts up everytime, no hotstart issues
*12-15 inhg at idle, doesn't surge
*TPS is adjusted, per the plug by the map sensor, but haven't check resistance at plug

 

I would recommend reinstalling the bac if you kept a/c, ps, etc.

Have you checked your thermowax, or have you removed it also?

 

I don't currently have PS and A/C.

I have removed the thermowax and the double throttle from the TB

 

There must be a small vacuum leak. 12-15in Mercury isn't terrible, but it could be a little better on stock ports.

 

could there be a small vac leak and it still run rich like this? I temporarily pulled a nipple off and the afr went up to 11.6-11.8 and it seemed to run better and the idle picked up.

 

Many people would suggest keeping the BAC under most circumstances. Aaron Cake is a firm believer in this as he says removing it has zero advantages. Perhaps try reinstalling the BAC and see if that helps the situation any?

 

I will have to find one. I bought the manifold already blocked off.

 

did you ever figure out what caused this?

 

Not yet. I haven't been working on the car very much at all and been focusing on another project. Its still pretty rich and the idle will hunt when I put it in gear no matter how many times I set the TPS. I may need to get a new TPS as well as I still haven't gotten a BAC valve. Are you having similar issues?

 

some what it would start and be around 11.5 but if you hit the gas it will shoot up to 10.8 but the idle was pretty stable and like your problem my engine would shake.

 

Mine has been around 11 since its been hot outside, but I'm going to have to start testing/replacing sensors soon.... TPS, MAF, MAP, etc.

I'm using the 0-1v simulated out on my WB for the O2 sensor.

 

Added a BAC and plumbed a line into my TID behind the MAF. Little to no effect.

When the car first starts it idles at 700-800rpm. If I touch the gas it will catch at 1200-1300rpm, but using the clutch I can drop it back to 800rpm. Does anyone know what causes this plateau? I've seen this on every FC I've had and most that i've been around, especially with the stock ECU.

 

Also, when warm, I can put in into gear and the idle will start to hunt, like its the TPS. What changes does the ECU make when it senses that it is in gear?

 

most swaps don't wire in the 2 step fuel pump relay just behind the RF headlight. try checking to see how many volts your fuel pump is getting at idle, if it's above 9.3 volts then your pump is doing too much for the stock fuel system at low RPMs.

 

interesting Karack... I'll check that out. Is the turbo fuel relay setup different than N/A?


**I've band-aided the problem by pulling fuel from the stock map idle region using my Rtek 2.0. It idles great at around 12-12.5 AFR with only the occasional bump from smooth idle, if any. The idle plataeu seems to be gone as well.