High idle problem
Hi Guys. Have read the posts about this, especially the one labelled " Latest IAC adjustment instr. from Fitech turning both blades.
I've followed these, checked the TPS etc etc. Still no joy. 30003 unit on a Rover V8 (Buick 251). Latest software and new install of ECU + updated loom with fuse block (thank you Fitech - mine was out of warranty but you sent me new gear anyway 🙂 )
Anyhow.. engine runs fine but warm idle (set for 750rpm) won't go below around 1000.
Both front and rear throttle blades on their stops with no adj screws touching. The front blades actually slightly stick closed when on the stop (ie no adj screw touching).
TPS is zero. IAC mostly at zero with flickers to 3 . (Odd, with my old knackered ECU I could change the IAC with subtle tweaks of throttle stops)
Fitech Tech suggested a vacuum leak somewhere.
So, I have : Edelbrock manifold with a vac port up front. This is stopped off with threaded plug + tape + thread sealant.
On Fitech, forward facing vac port is closed off with factory nipple cover thing.
At the back, one of the two large vac ports is closed off with factory nipple thing. The other feeds my brake servo.
Only two other pipes are the factory fitted one to the MAP sensor and the other to the distributor.
Today I've checked all Fitech bolts are secure, all intake manifold bolts secure.
Then I've got engine up to temp, idling and targeted all vac unions, servo hoses, nipple cover things, manifold joints and body gaskets with brake cleaner spray. Nothing changes.
I wasn't sure what brake cleaner would do but as a test I sprayed brake cleaner direct into air cleaner and engine started to die immediately then recovered.
So, if there are any vac leaks at joints/gaskets/pipes I would have expected engine to stumble a bit but nothing changes.
Is the sticking front throttle blade a clue maybe?
Thanks for reading and maybe someone has some ideas as to what I can check next.
EDIT... Damn! just checked my photos of reinstall of unit with new ECU etc. found this photo of the body gasket. I didn't replace it with new one and can't recall if I tried cleaning it 🙁
Is this the culprit? maybe enough little air leaks to f**k up the IAC system?
sigh...
Neil, New Zealand.
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You should always replace the gasket, which is probably why you are idling high and your IAC is not between 3 and 10. But I highly recommend a Phenolic Carb Spacer to prevent heat soak. The spacer really helps with keeping the Fitech EFI cool and helps to prevent the ECU from going bad in the first place.
Quote from SodaPop on April 13, 2023, 7:19 amYou should always replace the gasket, which is probably why you are idling high and your IAC is not between 3 and 10. But I highly recommend a Phenolic Carb Spacer to prevent heat soak. The spacer really helps with keeping the Fitech EFI cool and helps to prevent the ECU from going bad in the first place.
Thanks. My own stupid mistake. I know better but at the time didn't have new one... will order heat isolator spacer too!
Hi. Just replaced the gasket and checked the manifold and unit faces were nice and clean.
No change at all. Still idling at ~1000rpm rather than 750 and IAC at zero with occasional flicks to 3
Before putting in new gasket I checked butterflies. Front pair were fully shut with adj screw wound off ie couldn't get 0.001 feeler through. Rear pair had 0.001" gap. There's no room for the rear butterfly shaft to move any further; its stop lever is hard up against the body.
Could the rear butterfly gaps be the source of my extra air?
thanks. N
Your IAC is set wrong and you are setting it up wrong.
Here are the instructions for setting up IAC properly from Fitech:
One thing I want to make sure is that the IAC is set correctly and that you set the throttle blades front and rear using both adjustment throttle screws. It is commonly done that this is set using only the front throttle screw and if it is not set with the back screw also it can create all types of issues. Here is the procedure to do that.
This will be done with the engine off and key does not need to be on.
- Disconnect the throttle peddle from the throttle body, so we know it is not moving or holding the throttle.
- Unscrew both front and rear adjustment screws so they just come off of the pivot arm stop.
- Starting with the front screw, screw the adjustment screw in until it touches the pivot stop and you just see the throttle arm/blades just start to move. Once you see this movement screw the screw in ½ turn (If the engine is pretty stout go ¾-1 turn in)
- On the rear screw we are going to do the exact same thing, screw the adjustment in until you see it touch and move then go a ½ turn (If the engine is pretty stout go ¾-1 turn in)
- This will set the blades close enough to start and warm up for final adjustment. We just want the engine to idle, if it is high that is ok until it warms up if it is low and wont idle go in a small amount on both screws until it will idle.
- Start engine and let it warm up to 170 degrees F then look at the IAC steps on your dashboard. With the engine running and the temp at or above 170 adjust accordingly. If the IAC is above 10 you will screw in both screws equally until the IAC steps falls below 10 but does not sit on zero. If the IAC steps are staying on Zero and the idle is above the desired setting you will unscrew both screws equally until the IAC jumps back and forth from a number under 10 but not staying on zero and the idle is at your target RPM.
- While you are making your fine adjustments keep an eye on the TPS value, if it goes above .5 shut the engine off and let it sit for 30-45 seconds. Start the engine back up and continue with the throttle blade adjustment.
- Reconnect the throttle cable/rod.
Normally when the IAC is correct it will jump between 0 and a number under 10 but never sits on 0 and the target/programmed idle RPM is met then the IAC is set.
Thanks Sodapop. I've just carried out the exact procedure described for initial setup.
My target warm idle is 750rpm
- After setting throttle screws to 1/2 turn in, engine starts and sits at about 1700rpm.
- After a few minutes engine warms up to at least 170F. Revs gradually drop to ~1400rpm
- IAC reads Zero with occasional flicks to 3 or 4
- Now I slowly wind out the front and rear screws.
IAC still reads same. - Eventually rpm settles at around 980 with the both screws wound out fully (not touching lever arms).
IAC still zero with flicks to 3 or 4 - TPS stays at zero.
Fitech tech said I must have a vac leak somewhere.
Made my own smoke tester and found no obvious leaks from vac ports, gaskets or brake booster/piping.
but there did seem to be some smoke coming from under the fuel rail on the right-hand side. hard to say exactly from where because very awkward to seal off throttle body with a large cap and loads of duct tape.
No smoke from around IAC solenoid, map sensor (under ECU) or throttle bushings but only other place could be around TPS sensor maybe.
I'll have to try smoke testing again.
Any guidance after all this?
cheers. Neil
Hi again. just read some recent FB posts abut high idle problems with reference to throttle butterflies. During my recent smoke test I took off the lid and duct tape over the body. There was a lot more smoke coming up from secondaries than primaries. I've probed with feeler gauges and found I can get 1.5 thou feeler behind secondary butterflies.
I've done the initial setup routine three times now, with shut down, wait etc etc but always have high idle.
Time now to reset/center/align butterflies and adjusting the x-connection lever so all butters are closed equally when no pressure on from adj screws.
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I would try replacing the IAC motor as it may be faulty. Have you checked to see if you are getting any codes on the handheld? Also check with a gauge to see if you are reading the right RPM on the handheld as the blue wire may be picking up noise.
I would also suggest to send the unit to Fitech to have it checked and serviced. May save you alot of aggravation...
Thanks all but I went for the simple approach. Engine ran fine on the road so no issues with rpm noise, earths, codes, starting, stopping. All I had was too much air getting in at idle. Full smoke test topside showed no leaks anywhere but there was more smoke coming from rear butterfly plates than fronts. Exhaust test did show up some loose joints down the rear end though 🙂
Front butterflies (plates) would stick shut when screw was full off so wound in screw just enough to avoid the sticking. 1.5 thou feeler gauge would not get past either front blade.
Rear plates didn't stick shut when full screw off. BUT a 1.5 thou feeler gauge would just slip in at centre rear and front.
So, worked out that the distance between cross connecting lever joints between front and back plates needed to be 'just a little' further apart to allow the rear plates to close up.
Very fiddly but doable in situ: remove tiny split pin behind rear arm joint. watch out for tiny washer falling off. Unscrew the elbow joint half a turn (red arrow in generic photo) and refit. Replace washer and wafer thin split pin (very tricky... needs tiny fingers!).
RESULT = FIXED! yay!!
Did the proper setup IAC routine when warmed up and now have correct idle of 750rpm with IAC around 4 to 8 and TPS of no bigger than 0.5
IAC results vary a little after throttle pedal on/off and after a restart but now always between 3 and 11.
Thankfully I had decided to stick with doing just ONE mechanical adjustment at a time. I left the butterfly plates and those torx screws alone as I couldn't detect any obvious 'not centered' problems.
GUIDANCE: just 1/16 turn of those throttle screws can make a big difference with IAC readings.
I marked out my screw driver handle with 1/8 turn dots so I knew how much turn I was applying each time.
Hope this helps others banging their heads on the wall with high idle problems. cheers. Neil
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