aksansai

iTrader: (2)

To start, let me give you all a prologue.

1992 Maxima GXE (VG30E) - stock.

Engine #1) At 225K, number four piston went out of round. 85psi on the compression check. Motor retired for a 32K VG30E out of a 94 Maxima. 155-165psi.

Engine #2) At 50K, front main seal blew - bled all the oil out of the motor. 100-105psi. Motor retired for a 5K VG30E crate (Engine #3). ~170psi.

When I installed #2, it fired up without problems but idled at about 1800rpm. I thought the IACV might be acting up on the engine, and swapped with my #1's IACV (#1 had no problems with idle). The problem was not corrected. I inspected the TPS - looked good, but swapped for #1's TPS anyhow. The problem was not corrected.

It would sometimes surge upwards to 2300rpm before hitting a cut-off and resetting back to 1800 - and then surge toward 2300rpm. Rinse and repeat. Put the ECU into diagnostics mode, closed the IACV, and was able to get the motor to settle down to 1100rpm (still not nice).

When engine was cold (sat overnight) - the car would not start. Not enough air. Put the ECU back into diagnostics mode, opened the IACV back to default - started the motor, then high idle problem re-manifested.

Took it to Nissan in Huntsville for a complete run-through to find out how to get the car to idle properly. I was first told it was some failure with the AC compressor (Wiking debunked that very recently). Over $300 later, idle was still not corrected. Nissan techs then said distributor was faulty and asked for $800 to replace it. Told them they were full of bull, demanded by $300 back and my original part.

Put ECU into diagnostics mode, retarded the ignition until the screw was stopped - car idled at 800rpm (I'm a redneck so I fixed it like a redneck would have). Problem: fuel economy wasn't up to snuff and initial motor response when pressing the gas had hesitation - expected.

I drove the engine like this thinking that I would eventually figure out the problem. Oil pump started to make a knocking noise - replaced it. Faulty front main seal blew - engine was ruined.

Came across a great deal on a virtually brand new VG. Bought it. Replaced the torn up motor. Fired it up for the first time and guess what??

High idle problem again. But sometimes the motor runs at normal idle. It's almost like the cold start mode never gets cleared when engine it up to temperature. It will continue to idle at about 2000rpm until it gets warm and then sometimes try to go higher before the rinse/repeat cycle.

Other times, it idles normally at 750rpm. #3 is equipped with everything attached to the heads and block (including distributor, IACV, TPS, etc.). I've swapped the TPS and IACV to see if the problem could be corrected - nothing changes the idle. I've tested for vacuum leaks - everything is good to go. I replaced the PCV valve when I installed the engine, and tested it again for good measure - everything is fine with that regard.

I talked with a mechanic about the situation - they said it's the computer. I inform them that the problem did not occur with #1 - then they are baffled. I talked with Nissan, they said ECU malfunction is very unlikely (they work or they don't). But they did say if the ECU was malfunctioning, mixture problem would be manifested throughout the RPM range (surging while accelerating, etc.). I have no such problem. Other than the idle problem, this new engine is perfect.

I've tested for leaks in the intake manifold and snorkel gaskets and have found none. Because even with the IACV fully closed and the throttle body closed, the engine at 1500rpm can accelerate the car to about 23mph with good pull. It's getting air from somewhere.

Something is common between #2 and #3 to have the same problem on two different engines. Very odd thing is #1 having no trouble idling and #2/#3 having trouble idling.

Any ideas?

internetautomar

iTrader: (30)

coolant temp sensor

aksansai

iTrader: (2)

Is this a guess? This is the sensor locating across the EGRC sensor, right? Have you seen this problem before?

What's the chances of two sensors on two newer engines being faulty?

internetautomar

iTrader: (30)

guessing is all one can really do over the internet.
but the CTS is what tells your computer when the car has warmed up enough to switch from open loop to closed loop mode.
the sensor itself may be OK but the connector/harness going to it may be corroded and no long passing the signal like it should.

Cliff Clavin

iTrader: (11)

my coolant temp sensor went out (along with a bad IACV) and my idle was totally screwed, I mean crazy. The combination of both not working really messed things up.

It also threw a code 13 (coolant temp sensor circuit) but nothing else. I replaced that and it went back to normal surging idle and high idle from my bad IACV.

You should take a look at your ECU and check the codes. If Internetautmart is right (he often is) you will get the same code.

BTW, the sensor is around $20 at NAPA...at least it was for my VE. It's possibly the same part, but double check that.

aksansai

iTrader: (2)

Computer reads "55" - no errors present. I do not have code 13.

I need help locating the sensor. The Haynes manual I got only lists the temperature gauge (yep, the one in the cluster) sending unit. It notes that other sending units exists - but no description where. When I went to purchase the coolant sending unit from AutoZone it had a different connector altogether and, according to the computer, was located on the drivers side part of the block near one of the cylinders (really helpful).

Anyone else with a VG that has replaced their sending unit??

I know Wiking has a picture of the EGRC and temperature gauge sending unit across from each other, but according to Haynes, that sending unit only controls the reading on the cluster and has no affect on fast idle control.

Ideas?

aksansai

iTrader: (2)

I replaced the coolant temperature sensor - nothing has changed.

What next?

Wiking

Btw. Youre my HERO: fourth engine and still want to dive into max guts...

Next forget the chiltonhaynes crap and see LINKS on my webpage for smtg better.

Next write down which parts HAVE NOT been changed. I guess harness has not been serviced, inspected? SMJ's opened? ECU connector cleaned? Are TB /IACV /rubber hoses original? ...IACV needs infinidecimal leak to keep idle high, for example its feed hose attachement.

Whattodo:
- Use liquid gasket for IACV input airhose etc. airleaks. Check that Main air input tubing, attachements has no holes?
- Take drivers side mudguard off to verify the harness condition going to cabin. I've seen one rotten harness [tHere] on a car that had taken a hit in erlier life...
- Clean ALL connectors; open/clean SMJ's (now see the LINKS...)
- Verify voltage level at batt & at ECU & at MAF
- Use TB & MAF that was used in the non problematics setup
- recheck all rubber hose connections, maybe one is missing.

aksansai

iTrader: (2)

I love this car. Throughout its tenure, it has kissed deer, mail boxes, curbs, vans, and a number of other things to try to keep it off the road. Still drives like a dream (except for idle, mind you ) I'm a fairly big dude (6'3") and fit very well in the seats.

I have and also purchased an FSM. I've been paying close attention to the EF Diagnostic procedures 1 through 3 (I believe).

Parts Original to the Car

ECU
Mass airflow
MAP
Harness
Fuel Pump
O2 Sensor

Parts Original to the Engine (came with)

IACV
EGR
Distributor
Fuel Injectors
Knock

Musical Part Swapping (swapped, but nothing changed)

TPS

Parts Replaced in the Latest Engine Swap

Engine coolant temperature sensor
All vacuum hoses
PCV

Have not had the wiring harness inspected. Did find out a quick way to see if the engine coolant wires (in the harness) was talking with the computer: unplug it - watch it default to fail-safe mode and turn fans on.

SMJ??

Inspected - no corrosion or oxidation.

Yes but with no cracks or evidence of dry rot. I believe this engine to be very young because all rubber on this engine is still very flexible and in excellent condition. Used colored penetrating oil around hoses to check for leaks - there was no presence suction.

Clarify - use RTV sealant between hose and brass fitting?

Will check.

Hmm... if I only had a driver side mudguard... fell off a few years ago. So I need to check the harness going into the firewall. Still strange that this problem only occurred after engine swap - right?

Still got to figure out that SMJ....

Okay.

MAF is the same with the original (no problem) setup. Tried original TB with new fresh gasket - no correction.

I've done this several times - again and again. Will check again.

Thanks again for your help and will let you know.

Wiking

The SMJ is a long shot - and true, why would it (or harness) change during engine swap? Does not fit the pic... But still, if you have not owned the car from beginning... SMJ is the harness junction connector (2pcs) at furthermost left PITA corner under dash, harness connectors with zillion pins.

IACV
The FSM warns nissan mechs NOT to open IACV. Thats lucky for millions customers - but it underlines how little leak will get u in similar swamp youre now... I just tsted what would happen when IACV thumb thick hose is taken off. Well, engine dies. Inserted i back, and idle was around 1500. STRANGE. Turned the hose ten degrees: idle dropped to 900 and been since there. The hose was/is really ok - but still had a minuscle attachement leak...



Whats left?
- Clamp PCV hose closed for test.
- What happens if you start to clamp IACV air input hose closed?
- Check TB adjustment, seals and that butterfly flaps are screwed tight.
- MAF (dont think thats the problem, but who knows...)
- Fuel pump or pressure regulator (dont think thats the problem, but who knows...)
- Upper/lower Intake leak (spray oil, water or whatever all over - to listen for a change)

I would bet on the intake leak (after IACV hose) ... If nothin helps, I'd take upper/lower intakes, TB off and reseal them.

Good luck, surely youre gonna win this one.

aksansai

iTrader: (2)

Update: I've been following EC/EF diagnostics procedures 1-3 to see if I can pinpoint the problem. Here's are some new results:

1. Disconnecting IACV/AAC from harness.
   
   No change in idle.
2. Disconnecting the O2 sensor from harness.
   
   No change in idle. It also did not throw a code in the ECU - normal behavior?
3. Pinching off the blow-by tube going to PCV.
   
   No change in idle.
4. Inspected all vacuum hoses for leaks at IACV/AAC with penetrating oil.
   
   No suction of oil into hoses. All hoses appear to be sealing well.

Wiking

Notes on 1.
- IACV stepper motor purpose: choke/open air input on demand. If engine warm, no changes (no revving, no A/C, No steering...) no need to adjust.

- if TB flap zero pos (2.) is too open, no need to open IACV stepper motor valve

Havent seen any info how this screw (2.) is to be set (!?). Anyways, I'd set it so that the butterfly's just will not touch the TB walls.