unstable idle

Post by **SPYDOR** » Thu May 22, 2014 9:50 pm

It's the under-bonnet fuse but don't worry about it as you have removed the negative lead, that has the same effect.

derrick1988 wrote:I completely agree spydor I fitted a cat back system to my a8 with a 4 1/2 backbox and my idle and low end revs are all over the place! and for the record I have no leaks at all just a malfunctionin cat so I imagine with all included that's the issue!

It's surely only the exhaust tip that is 4.5" which won't cause problems with your idle. What diameter is the catback system?

Generally speaking 2.25" (single pipe) is fine for a stock H22a8, 2.5" is good upto around 250bhp and 3" is good to about 300bhp. If the catback you had fitted is 3" for example, it would be losing you back-pressure on a stock H22a8 and therefore low-end drivability.

Post by **derrick1988** » Thu May 22, 2014 11:32 pm

Yeah your right I'm 99% sure it's 2.5 piping , 250 bhp is ideally what I'm after.

quarkhimself · Post by **quarkhimself** » Fri May 23, 2014 8:02 pm

i got the iacv out and cleaned it, it was quite dirty and now is really clean.i also had another look at the fitv, that plastic thing was tightened all the way, so i turned it 3/4 of a turn loose.i also removed the radio fuse for about 5 minutes.put everything back together and the temperature gauge reaches the half point without any troubles, but as soon as i touch the throttle it starts to go up and down again. this time it seems i made some kind of small progress because it only happens when hot after i touch the throttle and it seems like it goes from around 700-1200 instead of 700-1500.could this be related to the TPS ? is there anything i can do to test or fix the TPS ?

Post by **Merlin** » Fri May 23, 2014 8:15 pm

Did you bleed the coolant again?

quarkhimself · Post by **quarkhimself** » Fri May 23, 2014 8:22 pm

no, i will try that again monday, i need to go get some more coolant from the store.

Post by **Vtecmec** » Fri May 23, 2014 9:17 pm

It's surprising how tricky it is to bleed the ludes fully, next time you try, jack the front end up (or park on a hill), this raises the rad and will help get any bubbles out. It can take 3-4 attempts to get everything out.

quarkhimself · Post by **quarkhimself** » Fri May 23, 2014 9:33 pm

does anyone know where i can find one of these spill free funnels in the uk ? they seem to be really handy for this job. i've searched on ebay but the only ones i found had to be ordered from the US.
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Post by **SPYDOR** » Fri May 23, 2014 9:39 pm

Out of interest is the throttle body closing fully straight away? When I cleaned mine recently, along with the FITV I needed to loosen the throttle cable a bit as it became a little tight and the revs would take a while to return to normal before I did that.

If yours is still a hunting idle then it won't be to do with that but thought I would mention it just in case!

quarkhimself · Post by **quarkhimself** » Thu May 29, 2014 1:09 pm

today i replaced one of the hoses that go into the iacv, and bled the cooling system again.the idle is still going up and down when the engine is hot, but i noticed that if i disconect the electrical conection on the iacv the idle stops going up and down and the check engine light turns on. since the problem only happens when hot an if the iacv is connected, does this mean the exhaust leak is not what's causing the problem ? does this mean i need a new iacv ?

Post by **Merlin** » Thu May 29, 2014 1:22 pm

You should get your engine up to temperature and remove the intake piping. With the engine running block the upper hole of in the throttle body. Report back what happens. Your engine may try to stall out when blocking the upper hole (which goes to the IACV)

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