low rich idle

[jnybbad]

I got my car running yesterday and have a few issues. My dash is out so I dont have my MIL code light right now. I have the necessary gauges hooked up for engine health. Once the car gets past 1500 rpm it cleans up and runs good but stumbles as the idle falls then tries to die and idle rough. The car is pretty stock with bigger IC, 3" down pipe and open 3" exhaust, K&N airfilter, recirculating BOV, still has EGR, fuel system upgrade, stock electronics.

Idles at 500 rpm (low)
AFR is 10.0 at idle
AFR jumps around lean rich as I accelerate

This is what I did:

Set fuel pressure per TSRM, Aeromotive fPR walbro pump all DM lines.
tested and set TPS, Idle air control per TSRM
tested and set dashpot
tested water temp sender, good
tested cold start injector, good
tried testing MAF but not really sure if Im doing it right, TSRM says to check ohms across two terminals then gives a number of specs for different temps, but thats it??

What else would cause these symptoms??

It was all fine when I took it apart and I didnt modify any of the elecronics, all stock, I did clean it all real good before tear down so I think water may have damaged something?? Or something is stuck from sitting??

 

[3p141592654]

You need to extract the codes. Hook up the MIL and run the test.

 

[Dirgle]

Like 3p141592654 said you really need to get those codes. Also what fuel system upgrades did you do? Is it just the FPR, walbro, and DM lines. Did these DM lines include the J-tube delete?

You also might want to get rid of that K&N filter, the oil charge they impregnate the cotton medium with to help filter will kill your AFM quick.

 

[jnybbad]

Ok, took the advice and pulled codes. I got code 31. I tested the voltage at the computer per the TSRM and it was good. When I ohm across the terminals on the MAF I get an open circuit. If I'm understanding the TSRM correct this is the problem. Am I correct?

 

[jnybbad]

And yes I deleted the j- tube.

 

[Dirgle]

To avoid confusion the stock electronics use an AFM to meter the air. A MAF is a different method of metering air entirely. It can be used on a 7M via a popular piggy-back electronic. That is why you will see a MAF referred to on here. But if your on stock electronics then we want to check the AFM.
AFM (Air Flow Meter)
MAF (Mas Air Flow)
Two different methods of accomplishing the purpose, but since you can find both in the supra world it's good to distinguish which one were talking about.



For code 31 you want to start by first verifying the parameters shown here:

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=57

 

[jnybbad]

I am sorry, it is an AFM, and I did follow those recommended trouble shooting tips. I do have 5vat the ECU and the E1 ground is good.

Do you know if I tested the AFM correctly by testing the resistance between THA & E2 on the AFM? I got no reading, open circuit when i did.

 

[Dirgle]

THA & E2 should be showing a reading, however if there is an open or short between those 2 the the ECU will throw a code 24.

The AFM houses two sensors, one is a air temp sensor, and the other is an opto-sensor that uses a mirror and a vortex generator to meter air flow. The THA and E1 pins are for the Air temp sensor and a bad one will throw a code 24.

In the link I showed above there is a basic procedure for testing air flow sensor(code 31). Check the voltages for KS and VC(the test for VC is on the next page). Once you check the voltages get back to us.

 

[3p141592654]

Code 31, I figured as much. Does your multimeter have a frequency (Hz) function? That's what you need to diagnose the AFM.

 

[jnybbad]

Yes, can you tell me what I need to do?

 

[jnybbad]

THA & E2 should be showing a reading, however if there is an open or short between those 2 the the ECU will throw a code 24.

The AFM houses two sensors, one is a air temp sensor, and the other is an opto-sensor that uses a mirror and a vortex generator to meter air flow. The THA and E1 pins are for the Air temp sensor and a bad one will throw a code 24.

In the link I showed above there is a basic procedure for testing air flow sensor(code 31). Check the voltages for KS and VC(the test for VC is on the next page). Once you check the voltages get back to us.

I did do those procedures and got 5 volts on the VC and the KS terminals to ground. I also tested E1 to ground and it was good.

 

[Dirgle]

I did do those procedures and got 5 volts on the VC and the KS terminals to ground. I also tested E1 to ground and it was good.

Got ya, I miss understood when I first read that sentence. My apologies.

As far as measuring the frequency you take the reading from The KS & E1 pins. With the engine running, you are looking for a relatively stable frequency, and for it to increase proportionally with airflow. If the frequency is all over the place or non-existent it's a good indication that the sensor is bad. Unfortunately the sensor is a non-repairable item. Most cleaning agents that you can get off the shelf will damage or fog over the delicate mirror further.

P.S. One other thing you can check is the voltage on the KS pin at the ECU, this will verify that the wire harness is ok.

 

[jnybbad]

Thank you I will give it a shot this week. Also I checked voltage at the AFM connector and the ECU and both were 5v so Im good there. Is there anything else that would cause a code 31 ? I found a bad thermo time switch for the cold start injector as well, reading 75 ohms when cold. Expensive little guy, $155 through rock auto.

 

[Dirgle]

You sure your thermo time switch is bad? The're not known for going bad. It won't kick back down to a lower resistance value until the coolant gets below 15°C(59°F). Going by where you list your location as, its entirely possible that the coolant didn't get low enough to rest it, even if sat over night.

Also where on rock auto did you find that. I've looked before but couldn't find one, that could be handy to know.

 

[jnybbad]

I took it out and put it in the freezer for awhile, ohms never move. For the thermo switch I just did a part # search on rock auto and it popped up

 

[Dirgle]

I took it out and put it in the freezer for awhile, ohms never move.

Yeah that would do it. Bummer.

And I'll admit, I never looked under EGR vacuum solenoid for it, wonder why.:dunno:

 

[CyFi6]

Basically your CSI switch is stuck open which would prevent the CSI switch from being able to activate the CSI. While that should be fixed it isn't the cause of your problem/code so don't expect replacing that to fix it.

 

[jnybbad]

Yes, I know. Was just found because I was going through all the testing steps of the EFI. I got a different AFM so we will see.

 

[jetjock]

You sure your thermo time switch is bad?.

Having read the entire thread I doubt it's bad...

 

[jnybbad]

How did you come to that conclusion ? The ohms are out of spec and don't change under freezing to hot water temp changes. Just sits at 75 ohms.