Hi I have 99 lx 470 with 145000 miles that had a slight hesitation in its idle so I replaced the spark plugs and two of the coils that were dirty on cylinders 5 and 6. A couple of weeks later after some fun in the mud my idle started to get worse and I had a noticeable hitch in engine speed when accelerating very slowly from a stop. Throughout the rest of the power band the car drives beautifully and it doesn't even always do the hesitation from a stop just when I have been idling for 30 secs plus or so. I am stumped and all the repair shops I trust are booked out for weeks, I have replaced the spark plugs, two coils cleaned the throttle body, the valve on top of the throttle body I think it's the IAC. I don't want to aimlessly replace parts but I don't know where to go next. Also no check engine lights ever, no issues in general for the last 16000 miles I have owned the car
99 lx 470 idle and light load rough
- Thread starter Graham1
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- Thread starter
- #2
Any ideas?
Battleship
GOLD Star
Replace the rest of the coils, they can sometimes fail for a while before they set a code, rough idle is a common symptom.
I lean towards coil packs. Typical first sign of failure is a slight hesitation off idle up to around 1300 rpm at slow acceleration. Unfortunately, your truck won't throw a CEL until the coil fails completely. I don't advise ordering the eBay "value pack" of 8 coils for the price of one. Go ahead and get Denso or at least AutoZone Duralast coils (lifetime warranty). They will cost you $75-$85 each over the counter. I would pick up a couple as well as a OBD code reader if you don't have one and stand by for the inevitable failure.... You'll know when it happens. Usually within a few hundred miles.
- Thread starter
- #5
Thank you yea I just ordered 6 more denso coils, won't be here until Wednesday unfortunately, seems like I've had a rough idle for 3000 miles or so with out a check engine light
Any day now....
Did replacing all of your coils fix the rough idle issue?
- Thread starter
- #8
Yes! And cleaning the IAC and THrottle body helped as well
Great, I'll replace all 8 coils & new plugs this weekend. I've been chasing down a rough idle now for months after doing all the normal stuff like throttle body, MAF etc. Whats the IAC?
- Thread starter
- #10
That idle air control it's the little valve on the top of the throttle body, two bolts open it, mine was pretty dirty.
Oh you mean the TPS - throttle position sensor? I replaced that a few weeks ago along with the APPS.
trdcorolla
SILVER Star
This thread has been helpful, i've had rough idle for the past few weeks with a with hesitation on random slow acceleration like @Graham1 but no CEL. The CEL finally came on yesterday, I had 2 codes, first code is P0300 and the second code is the same code but pending P0300. Do you think new coil packs will fix my issue?
Typically, you will get P0300, random misfire and a P030# where #=cylinder number. Is the truck running rougher than before the CEL or about the same. About the same, I would look at plugs first. Much rougher running, coil packs. If you are replacing coil packs, you may as well do your plugs too.
trdcorolla
SILVER Star
Thanks @Dwight S , I do have a pending P0300, does that mean it's still hasn't figured out with cylinder has the misfire? The truck is running rougher after the CEL, like it's going to stall. I had the truck baselined about 1k miles ago (new everything except coil packs), could a 17 year old coil pack go bad slowly after a major tune up/timing belt?
Tune up has nothing to do with it. 17 years does. The symptoms you describe sounds like a failing coil pack. Typically will start as a slight hesitation from idle when cold. It progressively get worse until it fails. Typically you will get the P0300 and a specific code for the cylinder. Perhaps drive it around the neighborhood and recheck the codes to see if it has triggered.
Will say this, if this is your first, it won't be your last. They usually fail one behind another. I replaced 4 over the course of about 6 months but haven't had to replace any for about a year.
May be less stressful, but more expensive to go ahead and replace all eight.
Will say this, if this is your first, it won't be your last. They usually fail one behind another. I replaced 4 over the course of about 6 months but haven't had to replace any for about a year.
May be less stressful, but more expensive to go ahead and replace all eight.
trdcorolla
SILVER Star
I'll replace all 8 coils with Denso's and give an update after, thanks!
2001LC
SILVER Star
The leading cause of coil failure is heat. Spark plug gap widens with age/use. The wider a spark plug gap gets the more current it will pull from a coil. The more current pulled the hotter a coil will get.
Inspecting each old spark plug as replaced, can be revealing. Not only for wide gap pointing to coil that may be on last leg. But for other signs of issue with valves, guides, rings, head gasket, timing, fuel/air mixture etc...
Factory has different intervals recommended for changing spark plugs. The most conservative I've seen is Lexus at 60K miles, the most aggressive is Toyota at 120K miles for "emission reasons". I replace spark plugs at 90K miles with T-belts.
Inspecting each old spark plug as replaced, can be revealing. Not only for wide gap pointing to coil that may be on last leg. But for other signs of issue with valves, guides, rings, head gasket, timing, fuel/air mixture etc...
Factory has different intervals recommended for changing spark plugs. The most conservative I've seen is Lexus at 60K miles, the most aggressive is Toyota at 120K miles for "emission reasons". I replace spark plugs at 90K miles with T-belts.
trdcorolla
SILVER Star
Thanks @2001LC , my master mechanic friend who did my major tuneup always tells me what he finds while working on my cars. He didn't say anything about really dirty plugs. He said the only thing that concerned him was dirty transfer fluid and he recommends doing another drain/refill next time he works on the car and my driver side exhaust manifold has a small leak. I used OEM parts for the tuneup/timing belt service at around 96k miles on the odometer. (Currently just hit 97k)
2001LC
SILVER Star
With such low miles, indicates not driven much. Fresh gas and a can of 44K through the gas tank may help.
Ask him if he check the gap and resistance of the spark plugs. Also gap, new is 1.0 to 1.1mm, Max gap is 1.3 mm used (not adjustable on used).
trdcorolla
SILVER Star
I've went though 1000 miles of gas before the check engine light. I'll replace the coils (the spark plugs are purchased are OEM from my local Toyota dealer), next tank i'll throw in a can of techron complete fuel system cleaner(I have a big bottle of techron complete fuel system cleaner in my garage), would 44K be that much better to go buy a bottle?
