Rough Idle Help (1 Viewer)

[turboed83]

Hi everyone,
I have been a long time lurker on here and really enjoy this site. So informative and inspirational. Well I am not new to Toyotas but rather new to the 80 Series. I have wanted one for a very long time and happened into a deal about 6 months on a 94 Non Locked rig with 216k on the clock. Now I got it as a fixer upper and started going through it. Then I spelled my 3rd get 4 runner and began driving it daily. Now the reason for the post is I am having an issue with a rough idle. I have no CEL. Basically about 2 weeks ago the engine began to run very rough at idle, more pronounced idling in gear but drives normal. Only rough in idle. Idle is right at 650 rpm. Now I have got through and replaced a ton on this truck so far. Engine wise: Plugs, valve cover gasket, oil pump seal, front timing seal, fan clutch, water pump, all coolant hoses, thermostat, air filter, cleaned throttle body, magna flow single cat pipe, accelerator cable, adjusted tps. Now it has always ran extremely smooth up until two weeks ago. It ran like a swiss clock. About 3 weeks ago I did the oil pump seal and front timing seal, then I simple greened under the front and used my low psi pressure washer to blow it off. I'm not certain but I think it was real shortly after this that the problem started. So I went through every electrical connector and cleaned them and applied dilectric grease. No change. One thing I noticed is that since I have owned it, randomly when the fuel level gets below 1/4 tank I will get a CEL. It doesn't last and goes away so I have been unable to identify. Also, anytime I put fuel in when I remove the cap I get what seems to me like an excessive swoosh. I'm not sure these are related because it has always done this and just started running rough. I have inspected vacuum lines and electrical connections and cannot find anything. I just drove it for Thanksgiving on a 1400 mile round trip. It did great except idled like crap. So I am at my wits end and asking for the invaluable guidance of the board member. Any suggestions ??

 

[scottryana]

Cracks in the bottom of the intake tube from air filter to throttle body.

 

[turboed83]

I will check that. I have removed it a few times and it looks kinda rough. No visual obviousness on top. Thanks

 

[Jeeper]

For the excessive pressure in fuel tank:

Charcoal Canister - Great Option!

 

[turboed83]

Jeeper, thanks for the reply. I have already seen you thread. I think this is the problem for sure. But my truck has done this for 6 months and never ran rough. I may be wrong but I'm not thinking a plugged charcoal canister could cause a rough idle ?? I am leaning towards either a vacuum leak or a stuck open EGR. I have looked through everything and have not found any damaged vacuum lines. Thanks

 

[Jeeper]

Yes. Charcoal canister issue is not related to your rough idle. Just wanted to ensure you had an answer for it. Keep us posted on rough idle - agreed w vacuum leak or EGR stuck/partially open as places to start.

 

[turboed83]

Ok so this morning I removed the intake tube (throttle body to air meter) and inspected it thoroughly. While I cannot find any cracks that are leaking through it does appear to be pretty dry rotted. It seals well around both ends though. Then I went through every vacuum line I could find. I removed a bunch and I cannot find any leak whatsoever. So I put it back together and started it up. Idled fantastic for about 15 min so I took it for a 5 minute drive around the block and then it starts idling bad again. If i turn the ac on it idles up to like 800 and feels good again. I disconnected the vacuum line to FPR to see if adding a little fuel at idle would help and I barely noticed any idle difference.

 

[turboed83]

So the CEL came back on and I checked the code and it is showing DTC26 for air/fuel rich. And incidentally I did got a lot worse gas mileage on my trip over thanksgiving. Like 3 mpg less than last. I noticed that the exhaust does seem to smell rich. So I ohmed out the sensors and they test ok. But in my experience this doesn't necessarily mean anything. Also, my idle does get worse when engine fully warmed up. So does this sound like faulty 02 sensors ? They do look original with 224k miles.

 

[bicycleagent003]

I had an intermittent hesitation issue for months which drove me Bananas and which the local LC specialist couldn't observe or diagnose. It ended up being the fuel/air mixture (upstream) oxygen sensor. Given the age and miles on your vehicle, I suggest changing both oxygen sensors. You can get 2 Denso sensors on Amazon for about $85 total, and they are absolutely plug and play.

 

[ZackR]

I had an intermittent hesitation issue for months which drove me Bananas and which the local LC specialist couldn't observe or diagnose. It ended up being the fuel/air mixture (upstream) oxygen sensor. Given the age and miles on your vehicle, I suggest changing both oxygen sensors. You can get 2 Denso sensors on Amazon for about $85 total, and they are absolutely plug and play.

This just might be what I need to solve my warm engine hesitation problem (1100-1900rpm) and occasional low idle when warm (400rpm). It looks like the upstream denso O2 sensor on Amazon for the 94' is $143 (part 234-4520).

94' FZJ80 276k

 

[turboed83]

Yeah I think I am leaning towards replacing both. I just am having a hard time swallowing that price tag. I heard that only the OEM stuff is good. Something about the Denso ones on Amazon are not very good and harness is different ? I have bought everything OEM for this thing as the stuff is built with some of the highest quality i've seen but I would like to save $ if these are ok. I do not see both for 85$ on Amazon. Could you point me in the direction of part numbers ? I wish I could just hookup my Autel at work and get live sensor data like the OBD2. What's weird is even though I had an intermittent CEL I never had a change in it running until I cleaned off the oil leak and all around front axle. I liberally covered everything with Simple Green and used my weak electric 900 psi pressure washer. It's basically like a car wash sprayer. But as I already mentioned I have gone through every electrical plug and cleaned them out and coated with Dielectric grease.

 

[turboed83]

Also, I wonder if converting to the Magnaflow single cat would cause any issue with the O2 ? I have had the cat on for about 3 months with no issue. I removed the stock rotted out cats and used the Magnaflow unit. I welded in the flange for the second sensor. Also ZackR I do not believe there is an upstream and downstream sensor on the 94 OBD1. Both sensors are pre-cat and read separate banks. In the magna flow cat pipe sensor placement is inline after the merge of the two downpipes so each sensor is not effectively reading each bank of cylinders equally. So both sensors should be the same.

 

[harrydunn]

Any news on this?

 

[turboed83]

Any news on this?

sorry for thel late update. Since last post I have changed the plug wires, cap, rotor, pcv hose, breather hose, and intake tube as well as most of the vaccuum lines. The intake tube made a slight difference in running better. Problem is that it is a totally random occurrence. So, one day I pull out kinda quickly and I had the window down and heard some pinging. Now I've never heard it because I really never press the gas down hard like this. So I came back and pulled plugs and they looked good. So I decided to pickup a timing light and check the timing. Well it was 16btdc at baseline. Somebody had timing waaaaaay advanced. So I timed it correctly and it now runs a lot better albeit sluggish feeling. So i decided to run a few tanks of 93 and some gumout regane in it and it seemed to help. Now I still get the intermittent rough idle but my CEL alamost never comes on and when it does it goes away within a min or two. Now I still have not done the fuel filter because I am waiting to pull the upper intake and do the PHH, clean the intake and throttle body, vacuum lines under manifold and filter all at once. Plus I still think my 02 sensors are sub par. Does anybody know if the Denso 234-4520 is an OEM sensor ? Because these are much more affordable on ebay.

 

[Kevin8086]

I too have a rough idle but it also feels a bit sluggish everywhere while accelerating but I've never driven another 4.5l cruiser so idk what it's supposed to feel like. 315k on my new to me cruiser. No cel and no codes at all. I probably need to test the EGR and check the intake tube.

 

[Timpanogos Slim]

The denso part number is correct, i believe. And it's true that 93-94 o2 sensors are painfully expensively unique. There WAS a recall for 93-94 o2 sensors so you should check to see if you can get them replaced by the dealer for free.

On a '94 there is something like 10 feet of vacuum line in 3 different sizes. Several of them aren't accessible until you remove the throttle body. Additionally, some people have found that the vacuum hard lines on their rigs have been clogged with some sort of white powder. You can run a guitar string through the lines to clear them out if that is the case.

Another item to check is the idle air control valve - which many people would call an idle air solenoid except it isn't a solenoid at all (it's a stepper). You probably won't be able to remove it from the throttle body without first removing the throttle body from the intake manifold. I recommend having some socket head cap screws to replace the phillips screws, since that will make it more plausible that you can remove the IACV again without removing the TB. Should be able to clean it and reinstall it. The FSM has a procedure for testing it but i am not sure it makes sense.

Check the EGR valve and modulator as well. iirc one of the two has a foam pad under the cap that can degrade and cause incorrect operation.