Rough idle when cold - Running rich

[Pochie45566]

Hi guys, 

I have a 1978 280z that i recently picked up. It runs great and i’ve been enjoying it tons. Im glad to be a part of the community.

When I start it up when cold the idle sits around 500, misses and lopes a bit. It doesnt smell rich at idle but as soon as I start driving it gets pretty rich smelling. So I dont think it is the cold start valve? Once it is warmed up the idle sits around 1100. It is set like this to keep out from dying when cold. It has no problem starting at all, just running after it is started. 

I know for a fact that the AFM and water temp sensor are good. I have cleaned out the air regulator and throttle body. That seemed to help a little bit. The thermotime switch looks to be a bit corroded but it is only used at start right? So as far as I can tell eveything in the cold start system is working. Ideas on where to go from here? 

[siteunseen]

Welcome to the forum.

I'd say first to make sure the thermotine and the coolant sensor plugs aren't crossed with each other.  The coolant sensor comes off into two wires as seen below.  

Second guess would be the AAR needs cleaning or maybe check to make sure ut opens and closes with heat.  Drop it in some boiling water and make sure it closes.  It opens up when cold allowing more air in to raise the idle.  Yours seems right the opposite though?  Anyway there'll be 20 replies before the end of the day, you'll get an answer.

Here's a good write up on the AAR...      Thanks @240260280

http://atlanticz.ca/zclub/techtips/aar/index.html

[Pochie45566]

53 minutes ago, siteunseen said:

Welcome to the forum.

I'd say first to make sure the thermotine and the coolant sensor plugs aren't crossed with each other.  The coolant sensor comes off into two wires as seen below.  

Second guess would be the AAR needs cleaning or maybe check to make sure ut opens and closes with heat.  Drop it in some boiling water and make sure it closes.  It opens up when cold allowing more air in to raise the idle.  Yours seems right the opposite though?  Anyway there'll be 20 replies before the end of the day, you'll get an answer.

Here's a good write up on the AAR...      Thanks @240260280

http://atlanticz.ca/zclub/techtips/aar/index.html

Thanks for the quick reply. I have cleaned all the carbon deposits out of the AAR, it seems to work fine. When i pulled it out of the car to clean it the flap was just a sliver open. Ill put it in some hot water to make sure it closes. Could the corrosion on the thermotime switch possibly be the cause? I thought it turned off when it was done cranking so it shouldn’t affect anything past when it is started. Everything is leading to the AAR but it seems to be working on first inspection. Ill take a look deeper into it.

Edited October 26, 2018 by Pochie45566

[siteunseen]

From all I've read the thermotine is what you say, only for start up.  The connector was broken off mine and I drove the car for a few months fine.  I found a Z at a local junkyard and put it on but couldn't tell any difference.  I've read some people don't have theirs plugged up at all.  You can't find them anymore.

When you loosen the oil cap does it stumble, die down on the RPMs?  That's an easy way to tell if you might have a vacuum leak.  If it doesn't change the idle you may have a bad vacuum hose somewhere.  That accordion boot up front is bad to crack and leak causing higher idle.  If it gets air before the throttle blade it's higher idle, after it would be low and lumpy, IF I REMEMBER RIGHT!  I've forgotten a lot about the EFI car.  

Also cleaning the rotor button and distributor cap will help, replacing them even better.

Good luck.  Drum roll for Zed Head.  He's very helpful.

[Dave WM]

there are so many ways to go about this. 1st is get the FSM and check the temp sensor AT THE CONNECTOR for the ECU. the AAR should be about 1/2 open IIRC but again the FSM should show this. You will need to check methodically to get it working right. The biggest problem trying to diagnose remotely is there always seems to be some critical piece of information not given that can cause chases down rabbit holes.

The FSM is you best bet.

[Pochie45566]

temp sensor is alright. tests good and is brand new. When i take the oil cap it bogs down, so I don't think its a vac leak. have also checked with carb cleaner all over. No signs of a vac leak. 

[Zed Head]

11 hours ago, Pochie45566 said:

When I start it up when cold the idle sits around 500, misses and lopes a bit. It doesnt smell rich at idle but as soon as I start driving it gets pretty rich smelling. So I dont think it is the cold start valve? Once it is warmed up the idle sits around 1100. It is set like this to keep out from dying when cold.

 

9 hours ago, Pochie45566 said:

Thanks for the quick reply. I have cleaned all the carbon deposits out of the AAR, it seems to work fine. When i pulled it out of the car to clean it the flap was just a sliver open. Ill put it in some hot water to make sure it closes.

Sounds like the AAR is not working correctly.  That would explain the low cold idle and fast hot idle.  Don't put the AAR in hot water, it's an electrical device, it has a heater inside.  Connect 12 volts across the two pins.  It should close completely within a couple of minutes.  It should be about half open when cold.

The rich when driving problem could just be exhaust fumes leaking in through the hatch.  A common problem.

[Pochie45566]

Ill do some testing on the AAR but i'd bet its my issue. Now time to find a new one. 

I know bosch makes one, so did nissan. All the identical part numbers seem to bring up parts that are no longer made. I will go to a pick a part here soon and try to find one. Could look on L series datsuns, and BMW of similar era id bet. Or if anyone here wants to sell me one hah. 

Update: I found out that you can throw the AAR from a 300zx in there. I found one for about 50 bucks. Before I pull the trigger on the ebay listing here, i'd like to test mine. Still going to choose an original part over this if I can find it though. Bear with me here, but the test would be throw it in the freezer, connect it up to a battery, then watch the valve slowly go from half-ish open to fully closed as it heats up? But it needs to be on the battery during this whole process. 

Edited October 27, 2018 by Pochie45566

[Dave WM]

No need to freeze it, its not a cold weather valve, more like engine not warm valve. Back in the days of carb cars you would push the pedal to the floor then release, then start. Pushing the pedal to the floor was how the carb cars would set a catch on the butterfly valves and hold them partly open. This allowed the extra air (the choke provided the extra fuel) needed to start. The AAR does the same thing for FI just does not need you to press the pedal to set it.

[siteunseen]

Trouble Shooting

• If you suffer from a fast idle after the car is warmed up, simply use pliers or vise 
  grips to pinch off the hose between the throttle body and AAR. If the idle rpm 
  decreases then the AAR is not closing.

NOTE: Vacuum leaks, a faulty BCCD valve, stuck accelerator linkage, weak throttle body 
return spring or gummed open throttle body flap can also cause a fast idle.

[Pochie45566]

That is a good point. Its hard for me to differentiate between a fast idle and low idle problem considering the idle screw has to be pretty high to keep it from dying when it’s cold. I’ll check it out and report back. 

[Pochie45566]

I’ve been working on it. Still cannot figure it out. My AAR seems to be ok. It is slightly open when cold and closes when hot. Water temp sensor checked out ok. Could it be the New afm being out of adjustment?