Idle problems

[Axlerod]

Previously, my CA would idle at about 700rpm when cold, and the idle was very lumpy. I assumed this was because of a faulty temp sensor. As some of you read, my CA MAFS was also sending back 11v.

I put the ECU in diagnostic mode, and did not make note of where the pot was to begin with, and got a code for MAFS and Coolant Temp Sensor.

I swapped the MAFS (SOHC KA) and turned the ECU pot all the way counter clockwise.

I tried to start it up again and it wouldn't go. Unplugged the battery for 30 seconds, and gave it another try. It would catch slighty, and sometimes run for a few seconds, then die. Most of the time I'd have to help the motor along with the starter after it was catching to get it going, and then it would only run at 500rpm. Touch the gas and it would die right away.

Then I swapped the coolant sensor and there was no change.

I haven't been able to get the motor idling long enough to check the MAF voltage.

It must be getting fuel and spark, since it does sort of run... no way to check vac, but again it was running previously and stable at 700rpm.

Any ideas?

[dattodude]

So where is the ECU pot pointing at the moment? If it is on an end point, then it may be switching modes for debugging.

download the manual, and check that the idle control valves are not clogged up.

[Axlerod]

So where is the ECU pot pointing at the moment? If it is on an end point, then it may be switching modes for debugging.

download the manual, and check that the idle control valves are not clogged up.

The ECU pot was (and is) fully counter clockwise (out of mode selector). I tried adjusting it incrementally clockwise, and then resetting the ECU. At about halfway to the two little markings, there seemed to be a difference, since the car fired up right away and idled sort of well, then I pressed the gas and revved up shortly, then died.

I will check the valves... but previously the car was running fine, and had no problem revving to the failsafe mode redline.

[dattodude]

I don't want to sound like a d!ck, but does have you checked all your intercooler plumbing. If there is a leak, these are the exact symptoms you'd see. It will barely idle and die when revved.

Fuel pressure will also affect things. Can you hear your fuel pump prime up when key goes to ign position? It should buzz with a high pitch, and change to a lower pitch as the fuel pressure comes up to the required 36psi (~260kpa). Of course the fuel pump should switch off after it's period of 5 seconds where it gets up to pressure.

Pull out the spark plugs..if all 4 plugs are wet, then it's ignition.

These two or three things sound the most likely.

[Axlerod]

Hey dude,

Yeah man, I've checked the piping, and unless there's a hole in the SMIC or something, I can't find a leak. However, I have no way to test vac for certain. It was the first thing I looked for.

The fuel pump (walbro) primes and shuts off, and I make sure to wait until it shuts off before attempting to start it.

I'll see if anyone locally can help me out with a vac meter, and I'll go over the piping one more time.

I didn't mess with the piping at all except for the piece at the throttle body when I swapped the coolant sensors, and that was after these new problems presented. I'm only stumped because previous to swapping the MAFS and putting the ECU in diag. mode, the car idled stably at 700rpm (w/ and w/o MAFS), and revved to the failsafe mode rev limit.

I checked the ECU again, and it's STILL throwing 12 and 13. (but maybe I didn't erase the codes)

I don't want to sound like a d!ck, but does have you checked all your intercooler plumbing. If there is a leak, these are the exact symptoms you'd see. It will barely idle and die when revved.

Fuel pressure will also affect things. Can you hear your fuel pump prime up when key goes to ign position? It should buzz with a high pitch, and change to a lower pitch as the fuel pressure comes up to the required 36psi (~260kpa). Of course the fuel pump should switch off after it's period of 5 seconds where it gets up to pressure.

Pull out the spark plugs..if all 4 plugs are wet, then it's ignition.

These two or three things sound the most likely.

[240sxbobbis]

this sound similar to my problem

[r34 gtr]

unplug that maf and see if it will run. if so than at least youve narrowed it down. you may also want to turn the key to the "on" position and go around with a multimeter checking voltages into the ecu.

- tim

[240sxbobbis]

now i did unplug my maf and it would sound like its about to cut off when i connect i t it would run like normal but when i rev nothing so i dont know ...

[Axlerod]

Hi Tim,

Few developments:

I tested both of my MAF Sensors and they work fine. Looks like the 11v was caused by a short somewhere along the line, so I'm just running a cheater wire to the ECU. The temp sensor I swapped in was also bad.

I took out the plugs and checked them; they were very fouled. I cleaned them up, and I've gotten a good CTS.

I'll start it up again once I've got some good gas in there and I've locked down the short which is making my temp gauge go to full hot immediately.

The only remaining problem is with my TPS. I get ~1.3k Ohms when the throttle is closed, and ~6.8k at WOT. The FSM says it should be around 1k and 9k respectively. Is my range ok?

Second problem with the TPS is that the Idle Switch does not show continuity on the proper pins when the throttle is closed. I'm going to make a new thread addressing this specifically.

[float_6969]

It sounds to me like you've got some considerable electrical grimlins. Keep working on it, you'll get it.

I posted in the other thread in regards to the TBS/idle switch.

After reading this, it sounds to me like it needs replaced.

[datsunboy]

by the way, that pot.....turning it doesnt do anything.It is there for the sole purpose of selecting the mode the ECU is in.

[float_6969]

Supposedly, (I've never seen one this works on) you can adjust the idle by turning that pot.

[Axlerod]

Yeah, that's what the UK guys (SXOC) told me it was for.

My motor is from Hong Kong, so there is no o2 sensor.

[datsunboy]

pretty common missunderstanding that one.

Has anyone actually EVER accomplished anything with the pot other than for changing modes?

Im open to criticsm

[knightrider]

everyone says its for adjusting idle, maybe a fine adjustment but from all of the ecus that i see at work, non of them being ca18det ecus, mostly z32 and sentras. all of them have that pot at the same position. the common position is a half turn from the full counter clockwise position. 1oclock if your looking at it so you can read the sticker.