Specs: 3k on rebuild, 110 compression all around, working omp(I still supplementary premix) and when I bought the motor the seller told me the idle was off.


Okay, so I blew my motor 5 days ago, and either had to replace it, or lose my job by TODAY. Luckily I found a motor pronto, picked it up, and swapped it this weekend.


So here's the thing. Just like the seller said, the idle is off. despite using the idle adjustment screw at the top of the UIM, and the tps adjustment screw, the shitty idle persists. Not that much a problem.

The REAL problem is, when the motor warms up, and I step on the throttle(anything past 15-20% it quickly acts like a 2 step rev limiter. What the HELL is going on? secondaries? timing? wtf???

 

Did you use the metal lower intake gasket and if so did you follow the revised torque sequence and use moly grease as stated by the tsb for lim replacement ?

 

series 4 or 5?

could be a bad OMP, TPS or airflow meter. shitty idle is usually caused by vacuum leaks, shitty porting or a combination of crappy emissions removal steps/timing off. low fuel pressure can also be the problem, it could also be why the previous engine failed and is pointing you towards the main issue which is in the car itself.

 

Series 5, afm is good(worked fine 5 days ago on my old motor). I'm suspecting TPS mainly because the car idles at 1300. but sometimes(this happened about 3 times for 30 seconds each) it will drop to about 500 rpm and go back to 1300 if i rev it and "shake it off"..

another thing I should add is that the smog pump is removed, so the aux ports do not open(didn't have one on my old motor, and this motor didn't come with one(though I am looking into purchasing all necessary equipment to get this going) which would probably explain the weird abrupt noise around 3800 rpm?

I'm thinking the timing is off as well.. the exhaust note just sounds a little off.

 

check codes
check all main harness connections
check your TPS voltage sweeps and set narrow to 1v warm at idle (backprobe green wire)
check timing and adjust with the engine idling below 1k RPMs
check for vacuum leaks all around the engine with carb cleaner
check your spark plug wire routing to the correct plugs
check that all 4 plugs are firing with your timing light


if it persists with nothing found then disconnect the secondary injector clips and run the engine again and see if the hesitation changes at all pointing you towards a secondary injection issue.

 

Harness is good. Triple checked it last night.

TPS- awaiting a friend to come over at lunch, he works at a very reputable shop.

I will check vacuum leaks tonight.

Spark plugs are firing for sure.




A couple more things I want to add(sorry, I just want to be sure that you guys are aware of everything going on) : If I turn the car off and back on again, it will pull evenly(at idle) through the rpm range. shouldn't that point to limp mode? But I just pulled the codes and got an 11 for intake air thermo-sensor, 12 TPS full range, and 18 TPS narrow range. None of those would throw the car into limp mode though. I'm beginning to get very confused

 

these ECUs do not store codes so you need to catch it at the time that the issue is occurring.

most commonly an OMP goes into limp mode when the car is hot and driven under a load versus idling.

you can also disconnect the OMP and see if it is giving you the same symptoms pointing you towards limp mode.

 

Well I actually leave the diagnostic ground wire thing on so I can read the codes as they pop up. And those were the codes that I got.


I'm STRONGLY leaning towards TPS. I'm just waiting for someone to agree with me so I can stop worrying


Does it not seem like the TPS? I mean it has to be out of adjustment at least a little, I am getting codes for it.

 

yes it can be the TPS but without any voltage readings we can't know if it is or isn't your main problem.

if the TPS has a dead spot it most likely is the main cause.

being that both codes are popping up it most likely is a 5 volt reference or ground wire issue, so you're likely either not going to get a reading at all or you're going to get something way off like 12v pointing to an engine harness issue.

try disconnecting the TPS and see if it runs better for the time being.

 

****, I thought I said posted this already, But it's after-burning alot. like popping, shooting little flames and what not. If I let off the throttle in any gear, I get a steady "POP, POP, POP, POP..."

it will also pop, if I rev it in neutral and let go, but then it's more of a grumbling sound like a 'blumb blumb pop"

sorry for the very weird descriptions, but that is the best way I can describe it

 

Backfires can be caused by the TPS. Your ECU is likely not receiving a signal from the TPS which causes the ECU to default to a predetermined TPS level, which is full throttle.

 

i have seen bad TPS's cause weird drivability hiccups, on S5's. since its throwing a code, its a logical 1st step...

 

Well why would it act like it's hitting a rev limiter when I open the throttle up? it does some crazy *** ****.. almost like a 2 step. and if I roll on the throttle slowly, it accelerates normally until the pedal hits about 20% and then it just stops accelerating, and acts like it's hitting fuel cut or something

 

are your trailing wires on correctly..to the spark plugs?

 

Because the narrow-range sensor could read <1v instead of 5 which would trigger the stock fuel cut on deceleration. Or there is a problem with with the wide range sweep sensor basically making the two sensors fight each other. See "Duck-season, wabbit-season" episode of looney tunes for a more graphical explanation. And I'm purely speculating since we have no voltage readings to go on.

I understand you're pressed for time and want to use it most efficiently. But the list RotaryEvolution put up is pretty comprehensive. Instead of asking why, look up the test procedure so you can get through as much of it as you can while your friend is available to help.

 

we can't do anymore diagnostics here without any of those tests performed. there's no point speculating a million different scenarios.

 

+1

Do the tests and fix what it could be, process of elimination will eventually get the problem addressed.

Talking about it won't fix it, start diagnosing the problem

Rotary >Pistons

 

Going to do the tests as early as my schedule allows.

well I'm trying to get a list of all things I should check together, that way i can do it all at once. hence this thread.

By the way, I HIGHLY appreciate all the quick replies. I would kill myself without this section.

 

Good luck, I hope you get it running right.

Rotary >Pistons

 

You never answered my question. I didn't ask the question for my own health ya know

It's very often overlooked. Whether you used the metal or the fiber gasket determines what torque pattern and installation method you follow.

If you installed a metal intake gasket using the torque sequence in the FSM or haynes manual, you WILL have an intake leak you'll have a hard time finding.

 

So metal gaskets. No good?

Rotary >Pistons

 

does the 2-step symptoms happen with TPS unplugged? from your descriptions, your TPS is definitely bad or at least way out of cal, but it should drive normally with it unplugged, except for popping on decel. sounds like there may be something else wrong too, like vacuum leak, bad AFM, or a bad secondary injector

 

Ooops! sorry.. but no, not a metal gasket.

It's running okay now, just need to do timing, and set tps.

So on my way home from work yesterday, it finally threw the codes I was more or less "hoping" for. 20 & 27 for OMP. I have been premixing anyways, so I was actually HOPING these codes would pop up, which would explain the fuel cut.

I already changed out the OMP for a working one, from my old motor and voila! runs way better now. no more limp mode for me!


Not out of the woods yet though :X

it idles at 1300 at times(most), and 500 at times(way less often). I tried adjusting the tps via multimeter, but can't seem to get any kind of resistance readings I also tried playing with the idle speed screw on the very top of the throttle body, and all that did was either make it idle at 1500, or make it idle at 100 and shut off. there was literally like a micrometer of adjustment between 1500, and shut off, and I couldn't seem to find a balance in between.

I'm starting to think the TPS is fried :/


one question I have though, would off timing hurt/impair the idle adjustment ability?

 

not that i have ever seen. installed dry or wet still torqued to 17ft/lbs i have never had any issues. most issues are due to unclean or warped mating surfaces.

 

The metal gaskets are fine, they just leak if installed or torqued incorrectly which I've seen done a few times.