MCV20 V6 Bizarre Idle

[damiankaren]

G'day,

The car is an Australian 1999 Camry V6 automatic transmission, MCV20 series 1MZ-FE engine, 200,000km.

The problem is intermittant.

I noticed that after taking my foot off the gas on a flat or down hill road the car did not slow down.

Slip the transmission into neutral at 100km/h(60mph) and the engine remains at 2400rpm. Touch the brake and the engine returns to slow idle. Foot off the brake and the engine returns to 2400rpm.

Let the car slow naturally (without brake and with trans. in N) and engine speed slows from 2400rpm as though it is matching the car road speed.

Let the car roll from stationary down a long hill (trans in N) engine speed climbs with the car speed to 2400rpm as car reaches 100km/h(60mph).

Also, with car stationary with Trans in PARK or N idle is around 1000rpm rather than the usual 750rpm.

The IAC valve is the suspect. I have tested the coil resistances, normal. Checked wiring between ECM and IAC, no problems. Of course, have also checked cruise control, throttle cables, vacuum operated start idle-up. No problems.

When the problem is not occurring I have tried the DLC1 test and the IAC valve behaves normally. Engine rpm increases for ~5seconds then returns to slow idle. When the problem is occurring this test results in no rpm change.

Whether the problem is occurring or not, when stationary, the idle-up as a result of AC on or steering movement appears to work normally.

Otherwise the car is performing normally. Shifting patterns and performance are normal.

Any ideas appreciated.

From reading the forums an IAC clean seems to be the next thing to try. However, I always like thinking about these things for a long time before putting a wrench on the car.

Damian.

[damiankaren]

An update for those that are interested.....

I took the intake hose of the throttle body. Then I sprayed a large amont of throttle body cleaner into the IAC ports in front and behind the throttle butterfly. I also gave the throttle body a clean behind the butterfly, it was not very dirty. Started it. Gave it a few revs.

For three days the car has been performing normally.

Hopefully it was as easy as that!

While doing all this I noticed something interesting.

With a jumper wire connecting pins E1 and TC in the diagnostic socket under the bonnet the O/D OFF, ABS, airbag and engine lights were all flashing at about twice per second. I believe this indicates that these systems are normal and not storing any error codes.

After playing around under the hood investigating the idle problem I noticed that the engine light was flashing differently. Like an older car I once owned the engine light was clearly flashing a code sequence.

The gregorys manual I have says nothing of this. The manual only mentions the use of a computer scanner.

Anyway the I watched the flashing engine light and it was spelling out two numbers 2431 and 3341.

As a test I shut down. Disconnected the battery. Waited. Reconnected the battery. Started it up. Put back the jumper wire. The engine light now flashed at twice per second. With the engine running I disconnented the MAF sensor. The engine light came on. I used the jumper wire to check the code: 2431. Did the same with the IAC connector: 3341.

First question: Does anyone have a list of these codes? The gregorys manual only lists scanner derived codes like P0100 or P0505.

Next question: There is an OBD-II diagnostic connector near the steering wheel. Does anyone know if this model camry is OBD-II compliant? Has anyone successfully used a scanner to get error codes or check engine values live? If so what brand of scanner? I am led to believe that the Camry computer uses the ISO 9141-2 protocol. Does anyone know if this is true?

I have an AutoXray EZ-Scan 5000 (www.autoxray.com) that I bought when I was living in the USA. There it worked well with Toyotas, Subarus, Chevys and Fords. These were all OBD-II compliant. Of course, it does not work with the Australian Camry. The pins in the Camry OBD-II connector seem to be OBD-II compliant. It just won't talk to the scanner. Any ideas appreciated.

[damiankaren]

Ok, so everywhere I have read tells me that ECU diagnostic codes on a 1999 V6 Camry can ONLY be read with an OBD-II type scanner. This is BS.

The two 4 digit error codes I was reading (2431 and 3341) were in fact four 2 digit error codes. Namely 24, 31 and 33, 41. They were apparently grouped like this as that was the order in which they were first detected.

So what are they?

Take a look at some older Toyota ECU sustems and they report error codes by flashing the check engine light to spell out 2 digit codes.

24 Air intake temperature sensor O/C or S/C
31 MAF sensor O/C or S/C
33 Idle speed control valve fault O/C or S/C
41 Throttle position sensor O/C or S/C

These were all things that I had disconnected with the engine running when I was investigating and cleaning the IAC valve problem.

As an experiment I also disconnected the camshaft position sensor and got a 12 code and the EGR position sensor and got a 96 code.

12 No distributor signal to ECU (of course my car does not have a distributor)
96 I can't find this in any older Toyota documentation.

Has anyone experienced this before?

I have 2 digit error code lists for the 1996 and earlier V6 Camry and a partial list for the 1997 and later 4 cylinder camry.

Does anyone have a list of 2 digit error codes for the 1MZ-FE V6 engine specifically?

[brownyy]

Hey dude,

So much info! Nice! and thank god someone else has had the same problem as me. I have a 2000 Vxi V6 auto... i have also noticed the high idle, and weird things like that and thought it might be my transmission... the reason for that is when i put it in drive from N or R or P it engages very roughly, with a real hard Thud. That happens one in 3 times and is shitting me up the wall... i think it has something to do with the engine revving higher when i engage the transmission...

I also thought the high idle was some fuel thing once, when i was running very very low one day it idled high... not sure if that has anyhting to do with it...

the dealership near me (toyota dealer) said that toyota engine codes can only be read by one machine that toyota make and sell to the dealers to keep profit in house, but they havent always been right... Also i have noticed the OBD-II plug but have never tried it...

I've also heard about the shorting that Diagnostics connecterd to read out the codes, but i was led to belive that the codes were 4 digit... and that it reads out the P codes... Pretty sure i got that somewhere from this forum...

And as a trick, when i needed the codes read once (different problem) i asked the dealership nicely and they did it free of charge, but i have always gone there for service's etc and they are nice people.

Good luck and i hope you find out what is wrong because i'd be interested to hear what it is... I'm soon to try some in-fuel engine clearer type stuff if that makes any different i'll let you know... cheers

[brownyy]

hey dude;

after playing around with the T1 E1 connections i got:

2141...
or 21 and 41?
I'm thinking my TPS is stuffed so that lines up with your 41... do you know what 21 is??
thanks

[damiankaren]

G'day,

My list of codes shows 21 as #1 oxygen sensor.

[damiankaren]

Cleaning the IAC seemed to fix the problem. It did not. I just had a longer than usual period of everything working well before the intermittant problem returned as before.

I replaced the IAC valve. The problem stayed.

I'm all out of ideas on this one. Intermittant faulty wiring? sigh.

Can anyone guess why putting my foot on the brake returns engine rpm to normal idle? (See first post)

Maybe just one of the IAC control signals is being lost?

Could some other sensor fault be fooling the ECM into commanding a high idle that seems to be vehicle speed specific? At the same time not effecting the vehicle drivability, economy or causing a error code?

Thanks.

[damiankaren]

The car gets sadder by the day.

Now, idle while stationary is all over the place. Switching between 750 and 1000rpm at random. While driving I can feel the power surging.

Also, the car now jumps into top gear at about 60kph (35mph) and stays there regardless of what I do with the gas. Press the gas to the floor and it just chugs along. Unless I floor it from a standing start then it seems to behave normally. Oh yes, this is an intermittant problem too.

Also, while at idle if I slowly the move the throttle open the rpm drops (sometimes stalls) just past the fully closed position.

I checked the TPS resistance. Normal. However, I don't think it changes smoothly through the range. Hard to tell. If I gently tap the TPS while the engine is running the rpm jumps around (more than usual) and sometimes stalls. Will try swapping a working TPS this weekend.

Also, the ECU is now reporting an oxygen sensor heater failure. Of course, on the sensor that is under the car.

Maybe I should leave the keys in it.......

[damiankaren]

I pushed some sewing pins into the back of the TPS connector and watched the voltage being sent to the ECU. At throttle closed it was varying 0.5-0.75V in time with engine rpm. Touch the throttle and it would go to 0.2V, engine almost dies. Clearly it was stuffed. I replaced the TPS with a new one AU$89.

The idle problem went away. Throttle closed voltage was fixed at about 0.5V and increased smoothly as the throttle was opened.

Also! The original problem has disappeared! After being permanently present for the last few weeks the bizarre idle is no more. Of course it could be coincidence.

I did some reading of the Toyota manuals and I have this theory.

Normally when the throttle is moved from open to closed the ECU commands the the IACV to open slightly further and then slowly close. Something about getting rid of unburned fuel. The faulty TPS was telling the ECU that the throttle was constantly moving from closed to slightly open and back again when really it was not moving at all. If this happened at the right rate MAYBE the IACV was not closing before being told to open slightly more until it was fully open? Also, when everything is normal when the ECU detects the throttle first moving from fully closed injector duration is breifly increased. MAYBE this contributed?

In another experiment I forced the IACV to fully open. Engine rpm was 2400. The same value I had while driving.

Why then was the rpm not 2400 when the car was stationary?

Another theory: vehicle speed is used by the ECU along with other sensor inputs to calculate injector duration, advance angle and who knows what else. MAYBE vehicle speed resulted in a maximum calculated rpm that the ECU would allow the IACV to run the engine at? A value that decreased with vehicle speed? Drawing a long bow?

Why did the rpm drop to a normal value when the brake was pressed?

Easy. If the throttle is closed above a certain preset vehicle speed the ECU closes the injectors until a slower preset speed is reached then starts injecting fuel again (for economy and emissions). If the brake is also pressed the preset speeds are lowered. So MAYBE when the car was moving and the transmission was in N and when I was pressing the brake the injectors were shutting down to let the engine rpm return to throttle closed idle? Then, when I released the brake the IACV cycled fully open again. Remember the TPS did not reliably show the throttle closed condition so the ECU continued to think the throttle was opening and closing.

The transmission? Has been normal since the day it went wrong. I have found nothing wrong and have been unable to replicate the fault. MAYBE the TPS was not even showing an open throttle when this problem was present?

It is all a big MAYBE. If the car works normally for a month I'll believe it is fixed.

The faulty oxygen sensor heater can wait.

So ends a long car weekend.....