low rough idle on cold starts (1 Viewer)

[Kkxrw]

@Kkxrw After you pull the fuses to reset the ECU, how long are you leaving it? The engine will idle real low until it relearns all the critical parameters. I can't remember exactly what Toyota states but I know it takes a few restarts and a few miles of driving. You may have fixed the issue but haven't given the ECU time to catch up.

@Kkxrw After you pull the fuses to reset the ECU, how long are you leaving it? The engine will idle real low until it relearns all the critical parameters. I can't remember exactly what Toyota states but I know it takes a few restarts and a few miles of driving. You may have fixed the issue but haven't given the ECU time to catch up.

I have taken the efi fuse out for 20 min then put it back in. I have driven for a few days and no change in cold start performance. Still runs rough until it is warm.

Last night the cel came on (after checking again for a vacuum leak). I got cel:

12Knock Control Sensor signal.
41Throttle Position Sensor signal
71EGR System

It does not run any different just now the light comes on.

41 - The throttle position sensor is new genuin toyota. Wires are in good shape.
71 - i was spraying throttle body cleaner. Wonder if i got it on something?

Anyone have any ideas?

Thanks

 

[PZLCruiser]

a few years back I had a funny sputter and stumble when starting my 96 and did a bunch of stuff to it like you. Turned out after doing my O2 sensors and asking my mechanic buddy to plug in the ob2 to monitor the O2 he told me the temp sensor was bad. Was giving false readings for the first min or two. Replaced that and solved my starting issue. Worth checking it out.

 

[Kkxrw]

a few years back I had a funny sputter and stumble when starting my 96 and did a bunch of stuff to it like you. Turned out after doing my O2 sensors and asking my mechanic buddy to plug in the ob2 to monitor the O2 he told me the temp sensor was bad. Was giving false readings for the first min or two. Replaced that and solved my starting issue. Worth checking it out.

Which temp sensor? I just changed mine (right next to oil filter) on the engine and no change in performance. It still stumbles when it is cold.

 

[Irish Reiver]

Both temp sensors are in roughly the same region of the cylinder head. Check the diagram below (From the '94 FSM).

 

[Kkxrw]

Both temp sensors are in roughly the same region of the cylinder head. Check the diagram below (From the '94 FSM).

View attachment 2852875

I did the ect sensor (grey plastic with 2 wire plug part 89422-35010) . Could there be a problem with one of the other sensors on the block? Any way to test? Thanks

 

[ppc]

Have you opened up and examined the main wiring harness where it passes by the EGR? You need to look at each wire and not just the outside wrapping. There are many posts about this problem that have some good pictures as well.

 

[Kkxrw]

Have you opened up and examined the main wiring harness where it passes by the EGR? You need to look at each wire and not just the outside wrapping. There are many posts about this problem that have some good pictures as well.

I check the wires and they look to be in good shape.

Today i checked o2 sensors and vaf meter. Everything is in spec to fsm when measuring ohms

Still runs rough when cold. Once it reaches full operating temp it runs fine???

 

[PZLCruiser]

Both temp sensors are in roughly the same region of the cylinder head. Check the diagram below (From the '94 FSM).

View attachment 2852875

I changed the ECT Sender Gauge

 

[Kaosu]

Had the mechanic look over the car and although he didn't have time to compression test or leakdown test (Very late notice booking with a very busy mechanic) he identified a couple of possible issues that I will look into.

Firstly he noticed that the MAF was at one point siliconed back together and after talking to the previous owner it seems that at some point in the past a *backfire apparently caused some issues with the MAF. I took it out of the car and cleaned it out and checked the connectors and they all look alright however reinstalled and the issue remains. If the following doesn't fix the problem I will return to the MAF and try and source a replacement.

The second thing I will attempt is completely replacing the vacuum lines over the next couple of days and if that fixes the issue I will update here. The tubing is quite cheap per meter and it is looking a bit worse for wear so I will change these over and post results below.

*Now it is not uncommon for 1FZ-FE owners in AUS to have an AutoGas system installed and mine has had one installed in the past. These can cause some pretty major issues in the long term (this is why I ended up having to buy a new cylinder head). This is also apparently a very good way to get your engine to backfire and damage parts upstream such as the MAF sensor so I will be taking that all out as soon as possible.

 

[Kkxrw]

Okay thanks and good luck. Mine is a 1994 so no maf. It has a vaf and passed all tests. I ended up bringing mine into a shop too for help. Will report back....

 

[TWILLY]

My '94 had similar trouble; a stumble on acceleration and occasional rough idle when cold that would resolve once the engine warmed. Despite earlier cleaning the EGR valve, actually replacing it and some other parts in the EGR system (I'll look those up and report back) fixed the problem.

 

[Kkxrw]

My '94 had similar trouble; a stumble on acceleration and occasional rough idle when cold that would resolve once the engine warmed. Despite earlier cleaning the EGR valve, actually replacing it and some other parts in the EGR system (I'll look those up and report back) fixed the problem.

Okay thanks keep me posted

 

[SaturnAscends]

Had the mechanic look over the car and although he didn't have time to compression test or leakdown test (Very late notice booking with a very busy mechanic) he identified a couple of possible issues that I will look into.

Firstly he noticed that the MAF was at one point siliconed back together and after talking to the previous owner it seems that at some point in the past a *backfire apparently caused some issues with the MAF. I took it out of the car and cleaned it out and checked the connectors and they all look alright however reinstalled and the issue remains. If the following doesn't fix the problem I will return to the MAF and try and source a replacement.

The second thing I will attempt is completely replacing the vacuum lines over the next couple of days and if that fixes the issue I will update here. The tubing is quite cheap per meter and it is looking a bit worse for wear so I will change these over and post results below.

*Now it is not uncommon for 1FZ-FE owners in AUS to have an AutoGas system installed and mine has had one installed in the past. These can cause some pretty major issues in the long term (this is why I ended up having to buy a new cylinder head). This is also apparently a very good way to get your engine to backfire and damage parts upstream such as the MAF sensor so I will be taking that all out as soon as possible.

I don't understand why the gas conversions are so popular down there. It seems like any money you save on petrol you'd lose and then some on eventual repairs on burnt valves and the like.

 

[Kaosu]

When it was installed I could vaguely understand it because based on the prices of gas at the time a full gas tank would get you around 450kms for under $10 but as the 3rd owner of the vehicle and gas prices having surged from under 10c per litre to well over $1.10 per litre... I think the whole system will be removed soon! Haven't even thought about engaging the gas system since we put the new head on.... Not a chance!

 

[robnicko]

When it was installed I could vaguely understand it because based on the prices of gas at the time a full gas tank would get you around 450kms for under $10 but as the 3rd owner of the vehicle and gas prices having surged from under 10c per litre to well over $1.10 per litre... I think the whole system will be removed soon! Haven't even thought about engaging the gas system since we put the new head on.... Not a chance!

yeah, i remember paying 9.5cpl for LPG when I first converted mine and now 89cpl is 'cheap' but they still export it for much much less than we pay......when my HG went I put LPG seats in and all good, mind you it did just over 400k on LPG before issues

Do you have the intake pipe with holes in it and the 'stubby holder' over the pipe just before the throttle body? This is the safeguard in event of a backfire
Also, did your vehicle have flashlube installed for the LPG?

 

[Kkxrw]

Still idling rough when cold. It runs fine when fully warm.

I double checked the vacuum diagram and everything is routed properly and no leaks.

I checked the codes again and showing a 12 and 41. Any thoughts On how to address these coded?. The throttle positiob sensor is new...

 

[Kkxrw]

Still idling rough when cold. It runs fine when fully warm

I checked the check valves under the intake. All were fine according to the fsm

I then built a cheap smoke machine (with a soldering iron and baby oil). When the engine was cold i pumped smoke into the system at the brake booter line. Smoke leaked at the top of the egr modulator. Is that normal?

 

[Kaosu]

Ended up replacing the entirety of the vacuum hose loop and no change there unfortunately but the hoses are nice, new and bendable again aha
If I come to a conclusion I will post it here

 

[Kkxrw]

Ended up replacing the entirety of the vacuum hose loop and no change there unfortunately but the hoses are nice, new and bendable again aha
If I come to a conclusion I will post it here

Thank you. I have not figured this out yet. My truck still runs rough at idle. I replaced all hoses and no change. If i reset the idle ( let truck get warm, turn off, put on 3 times then start) the idle will smooth out. If i figure this out i will post the solution.

 

[BILT4ME]

Thank you. I have not figured this out yet. My truck still runs rough at idle. I replaced all hoses and no change. If i reset the idle ( let truck get warm, turn off, put on 3 times then start) the idle will smooth out. If i figure this out i will post the solution.

From all I have read on here, it would point first to (3) things:

Temperature Sensors in the head (You've recently done one)
IAC valve operation.
VSV valve operation.

As I think about what you have done and tested and what changes when the engine comes up to temp:
ECU goes to "Closed Loop" and the fuel pump changes speed. This is determined from the temp sensor.
This also changes the O2 sensor limits the ECU monitors.

Vacuum leaks could be a source, but unlikely.
Does the engine die or get REALLY rough if you remove the oil fill cap while running? It should get REALLY rough and nearly die when you open it. If not, you have massive vacuum leaks the ECU is already adjusting for such as valve cover leaks and/or spark plug tube seal leaks.

Possibly check fuel filters both in tank and under the intake manifold.

Check fuel pressure at idle prior to warm-up and again after warm-up.