Mechanics

NISSAN MAXIMA ENGINE PROBLEM

1991 Nissan Maxima • 200,000 miles

Just replaced the ECU, screw set to anticlockwise, disconnected battery took it for a drive to learn engine, there is a intermittant injector mis on quick acceleration when I back my foot off slowly it runs smooth. Idle is smooth in park, but hesitates in drive when stopped at the lights fluctuating between 900/500, under load perfect no fluctuation, cruise control runs perfect on open road I also replaced the MAF, spark plugs, fuel filter, oil changed and filter, spark plugs appear to be running lean, whereas before the problem with the prior ECU were running very rich,
There no vacuum leaks compression is 160 each cylinder, coolant sensor works, timing is spot on, doesn't overheat. Original ECU put the car in limp mode after diagnostic would not reset.
check engine light sayed on all the time. No light now.
Question do I have to adjust the IAC, I think some mechanic played with the screw under the black rubber on top of the IAC prior to all of this, the reason I ask it appears that ECU is not in control at idle because when I engage the A/C no revs changes are noticeable whereas before all of this drama it did up the revs at idle. If this does require adjustment I know that screwing that screw all the way clockwise shuts off IAC. Do you know if this would work by then turning the screw anticlockwise until 1000 revs is acheived. If so can I just adjust this with the igntion off then starting the vehicle and repaeting same until 1000 revs is achieved. Or do I have to disconnect the soleniod and do it with the engine running.


Regards
Kevin
Avatar
Kingham
February 23, 2013.



Iac gets a signal from the ecu to maintain a pre determined idle so it will not stall. I have never had to adjust one as either the iac was defective or carbon in the passages was the culprit. As far as the screw goes, try backing it out till ti gives about 100.

Did you have the injectors professionally cleaned? Additives rarely work.

What about the cap, rotor and wires?

Roy

ASEMaster6371
Feb 23, 2013.
Yes all done prior to the original ECU not being able to reset. Roy so many prof experts looked at my engine and all threw the towel in after a couple of days, with no solution, I had had enough of all that advice. All my vehicle had done was go into limp mode and no one could get it out. Nor being a fully imported model in Australia did many have the actual ECU, I found it by chance, the actual one. All my information I have got mostly from America and the web.

I have a reading for MODE 11 Run the engine above 2000 RPM under no load while looking at the
ECU.
If the RED LED blinks simultaneously with the GREEN LED, the
air/fuel mixture is modulating properly

If the RED LED stays off, the mixture is more than 5% rich.
If the RED LED stays on, the mixture is more than 5% lean.
Both these conditions indicate a fault elsewhere that needs further
investigation.
I know how to get mode 2 and then do the above, mine states lean, then you read other sites some say release the inlet clips on the MAF intake side, because the Nissan Maxima on my model and year will only operate correctly with the original air filter. What was quite constant is to disconnect the soleniod on IAC adjust the screw to get base idle and then reconnect soleniod. It further stated that if the IAC idle is to high then it would run engine and not the ECU, does that make sense to you Roy.

If it hadn't have been from all this research my vehicle would still be in limp mode with a bad ECU you see unless it is obd11 no one knows how to read the codes on old a technology plus Maxima's in Australia didn't start until 1996. Anyway at least it is running smooth on the highway. Any suggestions on how to bring idle up when stopped at lights will be appeciated

thks
kevin

Tiny
Kingham
Feb 23, 2013.
Thanks Roy

Fixed unhooked the solenoid from the IACto the ECU brought up the revs by adjusting plastic screw body. With all things on A/c lights etc had it running at 1000 rpm. Connected back up ran it for 4 kilometres stopped at lights and side of the road in drive all electrics on 750rpm never missed at beat, all electrics off 1000 rpm never missed a beat in neutral 1000 rpm never missed a beat. Screw set 4.5 turns anticlockwise from base, base being completely closed.

Thanks again
kevin

Tiny
Kingham
Feb 24, 2013.