HI, I have an STi 5 Type R which has been TEK 3'd by pat for about a year now (other mods are decat system, hks ssqv, itg panel filter, uprated fuel pump), pat came out the other night to tweak the map (run more fuel in higher up the rev range, and puty on the low-octane safety map), and since then, on warm idle, the car is hunting. at first we thought it was the MAF sensor knackered, but pat has said all seems fine from the voltages reading back if slowing down dramtically (i.e. from 2krpm to idle, the car will almost stall - and sometimes does, if slowing down gradually, it appears to idle a bit better!

He did mention that I may need an uprated fuel pressure regulator.

I have just checked for fault codes, and there does not appear to be any!

Any ideas please - this is doing my head in!"

 

A slowly under reading MAF will be compensated for by the ECU - reflashing and then resetting ECU will cause this symptom, especially if in conjunction with a knackered lambda. I'd try a friends MAF and lambda. In really bad cases I've also had to strip and clean idle air stepper motor to get a nice idle back.

Richard

 

Pat thought it may have been the MAF, but on running the car, and using the log facility, all appeared fine with the MAF (when on boost and when idling), he seems fairly convinced it is the FPR (possibly having probelms due to the uprated pump), is it feasible that it is the FPR?

 

Anything is possible, but I'd have thought a faulty FPR would also give (big) problems when running WOT with boost!

Richard

 

OK, so it looks like I will be replacing both FPR and MAF sensor (as symptoms point to this - and if it doesnt solve it, at least I will have some piece of mind) - where is the best place to get a MAF for a MY99 STi from, what is the part number and how much can I expect to pay?!?

 

I can help with the part number which is 22794AA010, however not being in the UK, I can't help on where the best place is to buy from. I believe the price ranges from 68 to 80 pounds.

 

Any Subaru dealer should be able to supply for about £75. Just remember to only order the sensor, and not the surrounding air ducting...

 

I also had similar idle trouble recently ( RB5 Tek 3'd ). After major headaches with my alarm, the ECU was reset umpteen times, the car started hunting / stalling at junctions. Checked pipework etc incase anything had been disturbed under the bonnet by the alarm fitters, and checked for fault codes which there were none, then booked it into the garage to get checked out. Had to wait 4 days,then the night before it was due to go in, the car settled down back to normal .
Now, i had been led to believe it could be the MAF sensor failing, so what i'm asking is, does the ECU compensate for a failing sensor, which means i still have a problem, or has it just taken 3 or 4 days for the car to settle back to normal after it's alarm troubles. The car runs superb again, with no hint of any trouble , but am i being mis led
It has been mentioned that engine damage can occur due to a failed MAF sensor , so i'd like to get this cleared up ASAP.

 

With a healthy car the worst you would expect after an ECU reset is that the car will fire up and the revs will drop slightly before it springs into a completely clean idle. This should happen only once and should behave perfectly after that.

ECU can indeed learn around a failing MAF, reset decompensates it.

A small change in MAF voltage produces a massive change in fuelling since the voltage is not anything like linear, so it is difficult to be categorical about normal voltages.

To check a MAF with Delta Dash I look at knock correction, engine load, lambda voltage, MAF voltage as well as air fuel correction.

 

New MAF ordered today, I assume I am best to reset the ECU when I fit the MAF? And if that does not cure it, then the lamda could be shagged?

Out of interest, would an uprated pressure reg actually give any performance gain to the car?

 

Badgerbell,

As a car feels faster with a leaner mixture, there's every chance your MAF is shagged. You say it's crap to begin with after resetting the ECU, but then gets better and better over the next couple of days? The ECU first of all learns it's way round the failing MAF, and everything starts to feel smoother. Then, as the ECU thinks there's less air going into the engine, it adjusts the fuel accordingly. The mixture becomes leaner and leaner, the car feels faster and faster... and then a piston melts.

If you had a Knocklink and/or an AFR gauge, you would have more of an idea if the MAF is knackered. First thing I'd do though is reset the ECU again, and see if you get the same occurrence...

 

thats it . i'm really worried now

 

OK, new MAF is now on car, knock link only ever lights green, if dropping the revs from >2KRPM to idle, needle drops right down, then recovers to ~750rpm and maintains a rock steady idle. Is the lambda likely to cause the initial drop in revs (and if so, can it be fixed, do I have to buy a new one, how much,, is there any tests I can to to test it?, will it cause further problems - i.e. expensive engine probs).

Car seems to run fine other than that!

 

im just about to do the same as u tony, maf will be fitted in 1 hour, my STiV with TEK3 is also dropping down past norm tickover then recovering, its not happening all the time but it is getting more frequent, good luck, will let u know my results

 

just a thought, disconnect your lambda & see what effect if any it has on your tickover

 

will the car run OK without lambda being connected? If it then drops to idle normally, can i assume it is the lambda that is knackered? If so, does anyone have a part code and how much am I looking at??

 

tony, it will be ok 4 the test, lambda circa £100 4 OE, some people go 4 the cheaper lambdas, (halfords etc) but i dont think they last as long