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Rough Idle - 2.6L 4ZE1

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Rough Idle - 2.6L 4ZE1

Postby WestOz » Thu Apr 24, 2014 9:48 am

I have an idle problem with my 2.6l 4ZE1 1995 in that it idles a bit rough. I have checked plugs, valve clearances, timing, vacuum hoses, replaced fuel filter, air filter, cleaned the MAFS, cleaned the Throttle Body and run a can of injector cleaner through (Toyota Stuff, which I am told is the best), all with very little or no change. Idle is steady at 900 rpm though it does vary slightly. I haven't checked compression, fuel pressure or the injectors, so could be one or more of those, she doesn't blow any smoke and seems fuel efficient (400km on a tank), she runs very nicely at all other rpms. Fast Idle works at cold start up and when Air con is switched on, so I believe those parts are working ok, though they do seem to leak a little vacuum when checked but it is very minor and a finger over the vacuum points makes no difference. I have not been able to locate the ERG valve and don't appear to have an exhaust gas take off on the exhaust or exhaust manifold that I can see, so not sure if its been removed or if there ever was one. Its not on the firewall end of the manifold which is where I think its supposed to be.

Any other thoughts? Should I pull the injectors and clean them in an ultrasonic bath with new filters and seals or am I looking for something else?

Cheers
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Re: Rough Idle - 2.6L 4ZE1

Postby geeves » Thu Apr 24, 2014 2:35 pm

there are so many things that can make a petrol engine idle rough. If its only a little bet it might be best to leave alone.
Could be o2 sensor could be electronic ignition module could be ecu could still be the plugs. Plugs can be funny things They will spark properly on the bench but not in a compressed atmosphere so still could be the issue. I would ignore the injectors as good power and economy suggest a good mixture
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Rough Idle - 2.6L 4ZE1

Postby WestOz » Fri Apr 25, 2014 9:26 am

Thanks Geeves, dont I know it!!! The number of items I have checked over and I've still not found the cause. In addition to no ERG Valve I also don't have an O2 sensor. That I'm very sure of as there is no wiring or fuse in the fuse box for the O2 sensor, let alone no sensor on the exhaust. I also don't have a catalytic converter, which is probably why I don't have the O2 sensor. 1995 must have been just prior to all those items being compulsory on vehicles in Australia (possibly NZ as well). Even though I dont appear to have an ERG valve, if I look past the throttle body into the inlet manifold it does appear to have quite a bit of black build up (carbon???) that could be a result of exhaust feedback. But if thats the case where is the ERG hiding. If I had one I am sure it would be the cause of the rough idle. I think I'm with you on the injectors being OK, though I do have kits and the ultrasonic bath, so maybe I will do them anyway just to be sure they are eliminated. You never know, pulling off the throttle body to get to them might reveal the real cause. Hope you have a good ANZAC Day and managed to get to a dawn service. Cheers
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Re: Rough Idle - 2.6L 4ZE1

Postby geeves » Fri Apr 25, 2014 12:12 pm

Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Rough Idle - 2.6L 4ZE1

Postby WestOz » Sun May 18, 2014 9:07 am

I'm still trying to chase the rough idle down. I haven't done anything extra yet as I've been waiting for bits to arrive and I've been away. However I was wondering if a faulty fuel pressure regulator could cause a rough idle. I have yet to get a fuel pressure test done, which I'm sure would eliminate the pressure regulator, but I thought it worth asking anyway. My issue is definitely idle speed only as she runs very nicely up through the gears and at speed with no hesitation or lack of power, so fuel delivery seems to be fine.
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Re: Rough Idle - 2.6L 4ZE1

Postby WestOz » Sun Jun 15, 2014 2:14 pm

Well since my last post I have checked the compression, all within 5psi of each other at 160 to 165 psi. So that's not the issue. I have changed the plug leads,and pulled off the distributor cap and rotor to check for tracking or cracks. None found. I have changed the Fuel Pressure Regulator as well, also with no effect. So I'm really at a loss. I did note while doing all this that once warmed up and idling at the nominal 900rpm that she does vary the idle speed by about 50 rpm or so on a random basis. Does that suggest anything to the gurus? I am probably at the stage of removing the throttle body and giving it a proper clean and maybe pulling the injectors and giving them a clean while I'm at it. I really don't think there is much more I can look at. Fuel Pressure is still a possibility but it can accelerate up hill hard in 3rd gear with no misfires or hesitation, so I believe that's all correct. Still I may have to eliminate it.

Any other good ideas?

Cheers,
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Re: Rough Idle - 2.6L 4ZE1

Postby nb422 » Sun Jun 15, 2014 4:01 pm

Ive seen distributors arc across points when worn out causing a 'miss' and the fix was a new dizzy cap. Also check any ducting after the throttle butterfly to see if there is any cracking etc as a small air leak can cause rough idle.
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Re: Rough Idle - 2.6L 4ZE1

Postby gb89amigo » Sun Jul 13, 2014 7:33 am

WestOz,

May i refer you back to the vacuum hoses. Since the idle problem seems relatively slight, though annoying, in your case, it does not take much to effect the exact symptom described. there are hoses that extend to under the TB and somewhat difficult to access. Any of the vacuum hoses need only an equivalent to a pinhole size hole, to allow air in. Typically, hose ends crack/fray and cutting back or replacement corrects suspect ends. Look for hoses that should be well seated, but may have slipped. Look for other items a hose may cross over or under, causing a rub point, possibly the start of a stress area. I've had the same problem with idling, checked the hoses twice! The third time, really examined closely and found an overlooked hidden hole created by another hose crossing under the faulty hose. Use spray carb cleaner to help locate the leak. Hope this helps!

Cheers,

GB
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Re: Rough Idle - 2.6L 4ZE1

Postby Viking54 » Tue Apr 09, 2019 12:21 pm

My 4ZE1 was up an down on idle I replaced everything plug leads, spark-plugs, dizzy cap & rotor button, vacuum lines, checked timing replaced cam drive belt, cleaned throttle body, it still had rough idle. It turned out the MAF / "mass air flow sensor " was the issue with my engine, I tried cleaning it, that made no difference, so I replaced unit with a new one. Now engine idles well & runs perfect also replaced air filter with a K&N. So try cleaning your MAF sensor an air-cleaner element. if you have checked everything else also clean your Throttle body.. next thing I'm doing is to fit a Snorkle to give a cold air intake as the standard air box draws air from under l/h mud guard/fender so raidiant road temps create hot air so in summer day time driving I've found engine drops performance, however runs really well at night in summer when air is cooler..
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