So I recently removed the precat and main cat off my 87 t2 and replaced it with a 3" downpipe back to the stock y-pipe now the car is idling funny it goes up and down when in neutral and stays in one spot when in gear with the clutch in I checked the tps its right on it idled perfect before the exhaust just wanted to know if anybody else ran into this after a do install

Here's a list of mods

S5 turbo

Racing beat fcd

3" TID

3" downpipe straight pipe to the stock y-pipe and mufflers

Rats nest delete (idled fine after I did this prior to dp install)

Air pump removal acv blocked off and split air tube also bac left on and did not touch the throttle body

MBC

Idle only acted funny when I changed the exhaust didn't touch anything else at the time

Here's a video of it idling
Rx7 t2 idle after dp: http://youtu.be/KoGWk4TquDM

You can see when I put it in gear with the clutch in at about 13 seconds in the idle stays the same

Any input is greatly appreciated

 

Anybody?

 

Lower your idle speed down to 750. The bounce is happening because the idle speed is hitting 1500 rpm. It isn't directly from the downpipe install. Maybe a small vac line is knocked off and causing an elevated idle.

 

OK I'll try and knock the idle down and check for vacuum leaks shouldn't be too hard after the rats nest delete

 

it has leaned down a bit more , on a stock ecu ( s4 ) there is a trim pot near the AFM to adjust
on s5 there is an air bypass on the AFM to trim in


also you may find you lost an earth strap to the exhaust when you swapped things and funny as it sounds, it is necessary to remove earth offsets from the narrow band eugo

 

My 1988 FC RX7 Turbo II does this exact same thing as well. It started when I started upgrading it some. I did the RTEK upgrade. I have changed it twice and it does it at times. The car does this after the RPM comes down from the initial 2k then after the car warms up like this for a few it goes away. I have a downpipe as well on it. It would be nice to have that go away for sure, but it does after it has warmed up a little. It is just a little annoying. I know this doesn't help you much, but wanted to say mine does this as well.

 

Well I figured mine out by setting the idle down a bit idles perfect now at 750 no pops just smooth

 

Thanks for the input don't know why it went up just after the exhaust but it worked!!

 

Glad you got it figured out.

 

Air bypass on the AFM? I have never seen such a thing, mine is on the throttle body.

Also, how do you earth ground a car, I thought it is chassis ground?

 

If you just deleted the air pump and air control valve, I would check around the block off plate for a potential vacuum leak.

 

look closer.. s5 has a true air bypass for unmetered air on the AFM .. while s4 has a resister trim pot instead

both achieve the same thing


on the TB.. you have a throttle stop screw.. a TPS adjust screw,, and you have an ( metered ) idle speed bypass on the BACV

all different to what i described ( a method to enrichen his idle mix )

as for the earth, not sure what you are on about,, all modern cars are chassis ground/ earth
the exhaust has a link to the chassis to maintain zero voltage offset to the lambda probe which otherwise would have to earth across supper hot turbo or exhaust connections ( which gain resistance when hot )

ground offset of just fractions of volts will effect the lambda feedback which is trying to maintain around 0.5 V

 

I was just messing with you in regards to calling chassis ground earth.

As far as the idle air screw, I promise you, it is on top of the throttle body (S5)

 

and if you move it.. does it change mixture??
no.. it changes idle speed
( and also throws out the tps adjust )

if you move the screw in the BACv.. it also adjusts only idle speed
( the correct way, without upsetting TPS )

both of those will not have not changed the metered air count

all they have done is lift idle speed


if you instead look at the bullet type AFM.. there is a screw
and by screwing it in or out
it adjusts the metered air count , and thus ,, the idle mixture
( and much lesser effect on cruise and power )



apologies to OP. ( terrible internet connection couldnt view vid )

 

This is what I am talking about.

 

Where is that ground attached to the exhaust and where to the chassis?

Thanks!
-J

 

Might be the firewall near the wiper motor. That ground is either to the exhaust or the transmission.

 

there is usually one on the flange from the main cat to one of the heat shield bolts
,, sometimes i have seen them rigged to the lower gearbox bolt that corner

there should also be one on the RH side of the twin system,
.. rear of the car where the exhaust humps over the IRS axle
( tellingly, where exhaust should be the coldest and has least effect on resistance )

i believe the front one is also there to also prevent static build up to help the cat do its job
as well as limit exhaust corrosion

the factory didnt put them there if they didnt think they needed a consistent ground