Exhaust pops/rev hang issue
 

Hi guys,

Since I picked up my 05 STi, I've had this weird rev hang issue, which is weird because it's a cable throttle and not the DBW found in the later scoobs.

I took the car to Surrey Rolling Road for just a power run, where they told me the map needs tweaking as it's a little lean at the top end. Took it back down and had the map tweaked, and I asked about the rev hang. They said they couldn't feel it on the dyno, and they were right I couldn't feel it on the drive home. Over time however, it has come back. If I lift off the throttle there's a delay until the revs fall basically. This can cause gear changes to be really ****ty, and when it's cold changing gears can be even more sensitive because the revs will climb when I put the clutch in when going from 1st to 2nd.

Another thing that I thought was weird was that when in neutral and stood still, there are no pops and crackles when revving. However, when I stick it into gear and rev there are quite a lot of pops and bangs. Why would the car be adding extra fuel when in gear when stood still? If this is not it, could the car have a pops and bangs map somewhere buried?

Really annoying issue I've been trying to sort for ages.

Cheers
Jack

Are there any aftermarket switches in the cabin?

Nope, none at all. The only switches are the OEM ones such as wipers, DCCD etc.

Faulty NPS? Or TPS?
Did you get graphs from the remap? Power graph,AFR,Boost etc?

Is that Throttle Position Sensor? What's the other one? How can I test these? I can't see any fault codes on the ECU.

Yep, the graphs looked absolutely perfect. AFR, boost and the power/torque had no problems looking at them.

Yes throttle position sensor
And Neutral Position Switch.
There is a pretty recent thread on here about a member loosing his mapped in pops&bangs,no error codes showed but I believe he resolved the issue by changing the NPS.
It's a slightly different issue to yours but a faulty NPS can cause your fault.
You can test the sensors with a multimeter to see if they are working as they should be.
Also doing some datalogging(if you can) will show up any problems.

It could be it drove ok due to the mapper resetting the ecu,which clears the learning tables.
Can you reset the ecu? Can you datalog?

I had the exact same problem

Replace the front o2 sensor with a genuine part.

Explains the running lean, the pops and the rev hang.

Are you serious? I mean, it's not running lean anymore thanks to the map tweak, and I don't see any error codes on the car?

Do you have the part number at all?

I originally got a **** replacement part off ebay that only made things worse.

Then got a genuine denso from eurocarparts and it ran normally after that.

part number is 710800195 - That was for a blobeye STi UK btw

Doesn't sound like the fault i had,

My neutral switch was faulty then i fitted the wrong polarity of sensor,

I would only get the pops and bangs when in neutral,

I have since fitted the correct sensor, however if you do make the mistake i did you can change the way the ecu reads polarity in the map if you cba changing sensor again.

Yours sounds like its working as it does it when in gear,

https://www.scoobynet.com/engine-man...ange-help.html

^^^ My thread may make it clearer.

Not sure the OP has had pops&bangs mapped in,that's why I suggested the NPS.
Sounds like it could be a number of things causing the revs to hang judging by the replies.
I did have a similar problem on my classic but it was really bad,coasting off throttle was a mare,intermittent fuel being added.
Doesn't sound like the OPs problem as mine was extreme.
I found by logging throttle position that if I pushed the throttle cable by hand when on closed throttle then the value would change,I slackened off the cable a little and sprayed the cable with some lube which cure my problem.

I don't think it's as something as simple as the throttle cable, as it seems to go away after an ECU reset, but then comes back not long after. It's driving me nuts.

I am pleased I have dialed it down to being when it is in gear though. For example, when I'm driving, if I lift off and coast there's rev hang. However, if I accelerate and then lift off and immediately place it into neutral the revs drop as quickly as they should.

The front O2 sensor seems like step I could take, but the car runs fine other than the pops and crackles when in gear when revving.

Why have pops and bangs anyway?

It's a rally car :lol1:

Silly me for thinking it was for attention whores :brickwall

Only on bonfire night and special occasions,like someone driving up your bum..:lol1: