Rough Idle with New Spark Plugs and Coil Packs (2 Viewers)

[AverySimmons]

Hey guys! New here and new owner to a 1999 cruiser. I bought her about 2 months ago with 115k miles and has been great so far but started to idle rough a few days ago. The CEL came on and would flash when driving so we replaced all 8 coil packs as well as sparks plugs. Once replaced, the CEL turned off and it is idling better but still not 100% as smooth as it used to be. Any suggestions?

 

[AARONTLC]

Hey guys! New here and new owner to a 1999 cruiser. I bought her about 2 months ago with 115k miles and has been great so far but started to idle rough a few days ago. The CEL came on and would flash when driving so we replaced all 8 coil packs as well as sparks plugs. Once replaced, the CEL turned off and it is idling better but still not 100% as smooth as it used to be. Any suggestions?

Well, I guess a good question would be:

What code(s) showed up?

What spark plugs did you install?

OEM coils are an expensive endeavor, is that what you installed?

The reason I ask is that these vehicles are very sensitive to non OEM parts. They tend to punish owners who like to save money. My LC “Aaron” threatens to leave me stranded if I don’t tow the Toyota parts line.

Let’s start there and see what the others say as well.

 

[AverySimmons]

We did not get the codes ran, had the same problem on my friends LC that was resolved with new coils. So that might be our problem, all she shops are backed up so we were hoping to fix it ourselves.

The spark plugs were Autolite

The coils were Duralast.

Not OEM… might also be our problem://

Pictures of the two added below.

 

[Rhetoric]

I run Autolites in my Kohler K241 flat head. But I would never run them in a 2UZ.

Without actually checking codes you are just throwing parts at this thing in hopes of a fix. Scan it for stored codes. What “fixed” one Cruiser doesnt mean it will fix yours.

Be prepared to replace all your coils again with Denso as well as plugs. And triple check you do 18 ft/lb on the plugs with no antiseize.

 

[Rednexus]

Agreed - avoid non-Denso ignition parts on your UZ. As much as I dislike Rock Auto, that's the cheapest place to get them and they are probably cheaper than the Duralast ignition parts. I think they are around $50 a pop.

However it's totally plausible that you simply don't have one of the coil packs plugged in all of the way. I forgot to plug one of mine in when i checked my spark plug torque last weekend and instantly got a rough idle and misfire code upon startup. It was only running on 7 cylinders.

 

[Land Shark]

Look at cleaning that throttle body etc. as well

 

[diego355]

Check vacuum hoses from intake resonator are connected properly and are not cracked same with complete intake hose, that could explain the rough idle

 

[privatebri]

+1 on checking those hoses.
That caught me the last time I did this job.
Also sage advice going with Rock Auto for the 673-1303s.

 

[Mike NXP]

How about just disconnecting, let sit, and reconnecting battery. I recall after doing my coils it idled weird for a while in the driveway. A few key cycles later and it leveled out. Thinking about the simple solutions first.

 

[AverySimmons]

Hey guys! New here and new owner to a 1999 cruiser. I bought her about 2 months ago with 115k miles and has been great so far but started to idle rough a few days ago. The CEL came on and would flash when driving so we replaced all 8 coil packs as well as sparks plugs. Once replaced, the CEL turned off and it is idling better but still not 100% as smooth as it used to be. Any suggestions?

Hey guys! New here and new owner to a 1999 cruiser. I bought her about 2 months ago with 115k miles and has been great so far but started to idle rough a few days ago. The CEL came on and would flash when driving so we replaced all 8 coil packs as well as sparks plugs. Once replaced, the CEL turned off and it is idling better but still not 100% as smooth as it used to be. Any suggestions?

Update: My ECU failed. The problem had nothing to do with the ignition coils and we were told the Denso ones we have still look good so they are going back in. Also doing new OEM spark plugs because the old ones were looking worn out and after reading what you guys said about non OEM plugs I don’t trust the Autolites. Even though they are working for now.

Lesson learned: Always get the code read even if you think you know what it is. Thought I could get this done without it be in the shop for a week but I was wrong. And Stick to OEM parts, forget trying to save a few bucks.

She will hopefully be good as new by the end of the week! Thanks everyone for your help!

 

[Trunk Monkey]

Never heard of an ECU failing, how was that diagnosed?

 

[AverySimmons]

Never heard of an ECU failing, how was that diagnosed?

Took it to the shop and they ran the code. Just got it back with the new ECU and it’s running better than ever! A lot more power with acceleration than before.

 

[Trunk Monkey]

If the ECU had failed it technically couldn't send a code, but glad it seems to have worked out with the new one. Wonder what code they think it was.

 

[GremlinMobile]

Took it to the shop and they ran the code. Just got it back with the new ECU and it’s running better than ever! A lot more power with acceleration than before.

Sounds to me like you got taken. How much money did they charge you? 100% they didn't just have a brand new ECU for your 99 that they threw in real quick, reprogrammed, and fixed everything in a jiffy. It's not too late to cause a fuss over this and get our money back.

 

[Rednexus]

It's pretty darn easy to swap an ECU. Also it's very plausible that it had a soldered connection break or some other issue partially damage it. The ECU can be capable of running the engine with a connection or two messed up (it would throw a code but not brick the vehicle). I figured this out the hard way when splicing into my ECU wiring harness to install a WAT torque converter lockup switch - the instructions were for an Australian vehicle and I ended up splicing into the wrong wires (they were for the camshaft position sensors). My GX still ran but the dash lit up immediately. Luckily that activity didn't fry my ECU, or the WAT lockup module.

Over on the GX forum, folks have reported transmission fluid wicking up the wiring harness and damaging the ECU as well.

 

[hoser]

I've never swapped ECU's in the 100 but I believe the earlier years are more involved than the later years. @Mauser

 

[cruisin4bruisins]

After reading everything I'm inclined to think that shop may have taken you for a ride.

1. I don't see how its possible that replacing all the coils and plugs made it noticeably better but it was still a faulty ECU. To me it would make sense if you replaced those parts and the result was still the same rough running motor.
2. They were able to find and replace the ECU really quick, like abnormally quick. Yes its easy to reinstall the ECU but finding one is a different story. Usually places don't have one on the back shelf because they so rarely fail.
3. I don't think a failing/failed ECU could throw a code. Its possible the code could have been for something else and putting the new parts in fixed it but it all just seems like too much of a coincidence.

After writing this I feel like I should have a tin foil hat on lol it just seems fishy to me

 

[Rednexus]

It would be very easy to test the taken-for-a-ride theory if the old ECU is in-hand. Swap it out (which should be <1 hour) and see if the problems re-appear.

I've certainly witness shops try to take people for a ride (spent hours a few weeks ago dealing with the fallout after Subaru dealer tried to rip my retired mom off on some clearly unnecessary repairs), but there absolutely are plausible scenarios where an ECU could fail or have some other issue. It's usually worth giving people the benefit of the doubt.

 

[cruisin4bruisins]

It would be very easy to test the taken-for-a-ride theory if the old ECU is in-hand. Swap it out (which should be <1 hour)and see if the codes re-appear.

I've certainly witness shops try to take people for a ride (spent hours a few weeks ago dealing with the fallout after Subaru dealer tried to rip my retired mom off on some clearly unnecessary repairs), but there absolutely are plausible scenarios where an ECU could fail or have some other issue.

Yeah thats actually a pretty good point, if he has the old ECU I would definitely stick it back in and try it out. If no change then something is up. But I have a feeling the shop got rid of the old ECU, if they even took it out to begin with.

 

[GremlinMobile]

Yeah thats actually a pretty good point, if he has the old ECU I would definitely stick it back in and try it out. If no change then something is up. But I have a feeling the shop got rid of the old ECU, if they even took it out to begin with.

They probably told him there's a core charge for the old ECU so they're gonna charge him even more money if he wants it back!