Idles well cold and hot, but not in between

[76was124]

I've been trying to figure out why my 81 fi fires up well, (idling around 1200 RPM) for about 1 minute after start up and when fullly up to temp (190F) runs perfect. In between, the idle drops from 1200 rpm cold to barely 400 (dual relay dropping out) then back to 950 when fully warm. I bought a brand new aux air regulator, but it didn't make a difference. Any suggestions on where to look next?

[RRoller123]

test the temp sensor in the cooling fitting at the front of the head.

[76was124]

Hi Pete,

Been there, ohmed it out, replaced it, no change.

[Kevin1]

This sounds like a stuck/inoperable auxiliary air valve.
High idle cold for about a minute = cold start valve running.
Warmed up, good idle = normal good idle.
In between low idle = cold motor with aux air valve stuck in closed position.

My guess is that if you pinch off the aav hose to insure little to no air gets through it would roughly duplicate the problem you are having now.

[RRoller123]

That makes sense.

[76was124]

This sounds like a stuck/inoperable auxiliary air valve.
High idle cold for about a minute = cold start valve running.
Warmed up, good idle = normal good idle.
In between low idle = cold motor with aux air valve stuck in closed position.

My guess is that if you pinch off the aav hose to insure little to no air gets through it would roughly duplicate the problem you are having now.

That's what I thought at first,seemed like it was closing early, but AAV works as designed. Has a moon slice opening that fully closes when warm. I even bought a brand new one to be sure.

I noticed my used AFM has the plug out of the mixture screw.....if that screw has been messed with could that cause a similar problem? Running too lean at start..

[Kevin1]

That mixture screw doesn't (at least on my car) make much of a change unless it is turned several full turns. Since the warmed up idle is good the mixture screw is likely best left where it is. Since it isn't the aav I am stumped. I would at this point go back to basics - clean and chech grounds and connectors, make sure the fuel filter is good, and recheck for any air leaks. Those two things alone account for half the problems I have had with l-jet fuel injection.

[RRoller123]

Check that the throttle position sensor isn't holding open the throttle plate. It is very easy to incorrectly adjust it such that it holds the plate slightly open when the TPS is in its "full off" position. This would tell the ECU that the throttle is closed when it is actually just slightly open, which would be ok when there is extra fuel during cold start, and sort of ok when fully warmed up, and awful in between. Adjust the throttle cable with the TPS completely loosened, then adjust the TPS after that.

[rjkoop]

The throttle position switch adjustment fixed my similar issue...

http://www.fiatspider.com/f08/viewtopic ... 30&t=26724

[76was124]

Okay, now I am just getting irritated.....

i took a closer look at TPS switch and noticed it was a little finicky to switching correctly when throttle plate at stop. This was because the top mounting screw had previously snapped off, and the drill and re-tap wasn't perfect. This caused a limit to ideal position adjustment, so I drilled out the screw slot a bit which gave me more adjustment.

Reset the idle stop, idle screw and TPS on a fully warm engine, and everything was fine, until......

I let the engine partially cool down, temp gauge was 1/2 way between cold and 190.

When I went to start the engine, which took 2 or 3 cranks. ( it used to only take 1/2 to 1 full turnover to start) the idle was way low? (Around 500) which causes an eventual stall unless I help with applying throttle.

I will let it do a full cool down and see what it's like when it starts from a dead cold engine.

[azruss]

you have 2 screw adjust in the throttle body. The one on the right is the cable stop. The one on the left is a idle air adjust. remove this screw to see if the o-ring is in tact. If not, replace and set idle per Brad's tuning manual.

[76was124]

you have 2 screw adjust in the throttle body. The one on the right is the cable stop. The one on the left is a idle air adjust. remove this screw to see if the o-ring is in tact. If not, replace and set idle per Brad's tuning manual.

Yes, thanks, but I've been through the procedure many times before.

The problem is if I set the idle correctly around 950 RPM when the engine is fullly up to temperature, the idle will drop too far when cool (Meaning, not dead cold)

It idles fine around 1100RPM when full cold as the AAR works properly on a cold engine. It's the period in between, after the AAR closes as the engine warms, but before I get to full operating temp (approx. 190)

If I cheat and open the idle air screw up a bit more to keep the idle around 950RPM when in this 'between' state. A fully warm engine (I.e. Fan cycles). I'll idle around 1100 RPM without changing anything other than the engine temp being higher.

Right now I compromised, and have it running 900 when partially warm and just over 1000 when at full operating temp.

Maybe I am making a bigger deal out of it than I should, as it drives great, pulls strong throughout the rpm range. It it's just irritating I can't get it per spec as this was rather involved restoration, so there isn't allot that hasn't been serviced or replaced on the engine and FI system.

[azruss]

I, too, have my idle set on the high side. I did this by opening the idle air adjust just a hair. I found that if i adjusted to factory, my plugs would start to misfire as it set at idle and would drop the idle. It only started to do this about a year after i had the injectors rebuilt. I attribute this to old steel fuel lines that are beginning to clog one of the injectors. By keeping the idle up (1100), the injectors still squirts good. The other advantage to the higher idle is better voltage at night when lights and heater are on. I gave up long ago trying to get the idle down to factory spec.

[76was124]

I, too, have my idle set on the high side. I did this by opening the idle air adjust just a hair. I found that if i adjusted to factory, my plugs would start to misfire as it set at idle and would drop the idle. It only started to do this about a year after i had the injectors rebuilt. I attribute this to old steel fuel lines that are beginning to clog one of the injectors. By keeping the idle up (1100), the injectors still squirts good. The other advantage to the higher idle is better voltage at night when lights and heater are on. I gave up long ago trying to get the idle down to factory spec.

That's exactly what I am seeing, and I agree low voltage seemed involved too. It's as though a voltage dip drops the dual relay momentarily when idling below 1000 r p m.

Thanks I feel better now!

[sierraspider]

I had the same problem and pretty much went thru everything. Finally figured out my AFM flap was slightly bent. Tried the sanding thing, no help. Finally had my AFM refurbed by a company in Cal.(Only cost $195) They went through everything and warrantied it for 18 months. Car has never run better and is really reliable now. Long road trips are no worry. If it gets down to that being the problem and you want some info, PM me and I'll send info.

Good luck