alia176
SILVER Star
I'm curious too......
1FZFE Slight Miss at Idle (1 Viewer)
- Thread starter Indiana80
- Start date
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Overfueling can be caused by vacuum leaks.
Did they replace your spark plug tube seals and valve cover gasket when the engine was rebuilt? Spark Plug Tube seal can be a huge vacuum leak. How about the PCV grommet?
I also changed my oil fill cap, as the seal on it was hard as a brick and was allowing an air leak. All the little leaks add up to big leaks.
An overfueling can be caused because a vacuum leak is "unmetered air entry". This allows extra oxygen into the system that the computer doesn't see. Then when the O2 sensors see the gas mix, there is too much O2, indicating a lean condition, so it holds the injectors open longer to compensate, thus causing poor mileage and black plugs.
The vacuum leak could be from EVERY hose, gasket, seal on the engine. There is a certain amount allowed for by the computer and it needs to "relearn" the base parameters.
Fix all the leaks, then pull the EFI fuse for 5 minutes to clear all settings, then start over.
I clear my settings regularly, especially before a long trip (3+ hours). Because I DD my truck, it learns the setting based on in-city traffic and slower speeds. When I hit the highway, it continues o fuel it based on those levels and I get horrible mileage. I can see a 1-2 MPG increase when I do this.
Did they replace your spark plug tube seals and valve cover gasket when the engine was rebuilt? Spark Plug Tube seal can be a huge vacuum leak. How about the PCV grommet?
I also changed my oil fill cap, as the seal on it was hard as a brick and was allowing an air leak. All the little leaks add up to big leaks.
An overfueling can be caused because a vacuum leak is "unmetered air entry". This allows extra oxygen into the system that the computer doesn't see. Then when the O2 sensors see the gas mix, there is too much O2, indicating a lean condition, so it holds the injectors open longer to compensate, thus causing poor mileage and black plugs.
The vacuum leak could be from EVERY hose, gasket, seal on the engine. There is a certain amount allowed for by the computer and it needs to "relearn" the base parameters.
Fix all the leaks, then pull the EFI fuse for 5 minutes to clear all settings, then start over.
I clear my settings regularly, especially before a long trip (3+ hours). Because I DD my truck, it learns the setting based on in-city traffic and slower speeds. When I hit the highway, it continues o fuel it based on those levels and I get horrible mileage. I can see a 1-2 MPG increase when I do this.
- Thread starter
- #23
Thanks for all your input. I’ve wanted to make sure the fuel system was good, so that’s done. Injectors have been refurbed by Witchhunter, new plug seals, new VSV under the upper intake. All new vacuum hoses. New valve cover gasket. New PCV valve and grommet. Throttle body cleaned and new throttle body gasket. EGR valve operating properly and not plugged up. New EGR gasket. New plugs. Newer plug wires and distr cap. New ignition coil. New FP regulator. All OEM parts. All assembled now. Still getting sporadic misfire on cylinders 1,2, 5, and 6. Cylinders 3 and 4 are good. Dry compression test is good 175 to 180 on all cylinders. All wires at harness and coming out of ECU behind glove box look great. At a loss. Might just have to live with the bumpy idle. No codes to trouble shoot. MAF appears to be original and intake boot is not new but appears OK. I might throw some more $ at the boot, test it out, and if that fails look into Joey’s Landtank’s MAF. Is it possible the miss on only 4 of the 6 cylinders could be caused by cracked intake boot or old MAF? Maybe a cam timing issue? I should mention it runs great under load on the road. Maybe I just need to take it out to the bush and beat the hell out of it?
- Thread starter
- #24
I should also mention that I noticed the oil fill cap was leaking some oil around it onto the valve cover. The rubber seal on the cap was hard as a rock / dried out. I installed a new cap tonight and it seemed to idle a bit better although occasionally a few slight misses / hiccups that I could feel in the seat. I have not yet reset the EFI system since putting new oil fill cap on. Not sure if I need to. It only sporadically light misses when idling in park. If idling in gear, it doesn’t seem to miss. Also it only misses when warmed up to 170 or so on the ultra gauge and up to 181. I can’t seem to find any vacuum leaks and a smoke test shows no leaks. At a loss here. Going to try to figure out myself now since my mechanic is convinced there’s nothing wrong with motor internals. My next step is to pull MAF and and clean it out with MAF cleaner and check the MAF connections. If that fails, I’ll throw a new intake boot on it. I also need to double check that the engine ground is good.
Also, my mechanic drive it today to see if it misses under load. He said there were no misses when accelerating up to highway speed. But once he got to 60 mph and cruised on flat road, it showed occasional misses on 1, 2, 5, and 6. He believes it’s something electrical- possibly sensor related.
Bought my 93 new and have put most of the 235k on it. Bought our 97 at 105k and it now has 285k - about half of it with me at the wheel. I maintain both of them 100% - neither has been worked on by anyone by me, other than the 97 before I bought it and they're always overmaintained. My 97 has done that sporadically at idle, the 93 has never done it. It just feels like a single cylinder misfire to me and most of the consumable bits on the 97 have been replaced several times over except the plug wires. All 6 plugs have always come out nearly identical and I track that in my written logs.
Edit - both of them have had their injectors sent to Mr. Injector where they were flow measured, cleaned, then flowed again with paper graphs provided, so I'm confident they are not the issue on the 97. Back then I was sure the result would be a slightly clogged or dribbling injector. Nope.
Edit - both of them have had their injectors sent to Mr. Injector where they were flow measured, cleaned, then flowed again with paper graphs provided, so I'm confident they are not the issue on the 97. Back then I was sure the result would be a slightly clogged or dribbling injector. Nope.
- Thread starter
- #26
Thanks for input, IdahoDoug. On your 97, have you replaced intake boot and MAF? Those are two areas I have not addressed and I’m somewhat confident they are original to the 225K miles on my 97’s chassis.
I think I am one of the few who have replaced the MAF. My friend who I bought the truck from spent something like $700 on a brand new Toyota MAF the month before I bought the truck (mis diagnosis with something else, I can't remember). I also recently replaced my intake tube just for the heck of it.... My slight miss at idle is still there.
- Thread starter
- #28
Here are my plugs that I just pulled and replaced. They have about 5000 miles on them- at most- and smell a little gassy. This seem normal for a 1FZFE? I will say that after putting a new oil cap on the valve cover and resetting the EFI, the idle stumble seems to have lessened / become less harsh.
I'm chasing a similar miss in my 93. Is only started doing it recently, and it's doing my head in.
I changed plugs recently, and they weren't dark like yours. Mine were a nice dry pale grey
I changed plugs recently, and they weren't dark like yours. Mine were a nice dry pale grey
- Thread starter
- #30
I might be getting somewhere...severed O2 sensor wire (harness wire) to rear O2 sensor- fixing today. Just figured out I’m missing ground wire from back of engine to firewall. Part ordered from Toyota. I’m guessing that’s causing me some issues.
- Thread starter
- #31
Opening this thread back up. I realized my plug wires were not OEM (they were the cheapy Denso), so I replaced those with new Yazakis. Also put another set of Denso OEM plugs in. I had a co-worker properly repair a damaged shielded harness wire (lead to rear O2 sensor). Here’s what I’m still seeing on my local mechanic’s Snap-On tool: the misfires are still there in cyl 1 and 2, then move to 5 and 6, then back to 1 and 2. Never under acceleration, just at idle or highway cruising on flat ground. Here’s the weird part, the diagnostics streaming tool will show temp and timing readings that are normal then for a few seconds they will all default to cold readings, then back to normal. Would not know any of this was happening without this diagnostic tool. One very nice LC expert that I reached out to had seen this twice before- once due to LED bulbs installed installed in cluster and another where harness ground wasn’t connected to rear of intake runner. I don’t have either of these issues and am not an electrical guru. Anybody else seen any gremlins like this? I mention in another recent post that I’ve got a couple small chaffed wires at the dizzy harness plug that I’ll be fixing as soon as temps are comfortable enough to work in my garage. I can’t seem to find any other signs of damage to harness or other wiring.
Pull your distributor cap off and make sure everything is dry and put is back together and put the sealant of your choice between cap and the distributor. I had moisture in there everytime i would start my 80 up and it would miss until throttle input and driving. once i would get some heat in there it ran fine. Once i cleaned it and sealed it i haven't had it since. Might not be your problem but figured i would throw it out there.
- Thread starter
- #33
Thank you. My dizzy housing is nice and dry and well-sealed.
- Thread starter
- #35
Thanks for asking. I ended up taking the truck to another mechanic. They found a couple vacuum leaks plus the valves needed some adjusting. My engine harness had some damage that I was not aware of, as well. Truck should be done soon and I’ll update my rough idle, misfire threads at that time. Hopefully this work will resolve it.
Could you give us some more info on this tool? I would like to know if the stumble I feel is just the engine adjusting idle/timing or an actual misfire.
I hope to latest round of vacuum leak fixes and adjustments fixes your problems.
Thanks
I hope to latest round of vacuum leak fixes and adjustments fixes your problems.
Thanks
Would you mind providing an update? Did that work resolve the misfire?
I just acquired a 96 LX450 that sat for about 2 years. Local shop reported bad misfire before replacing valve cover gasket, sparks and wires.
Misfire isn't as bad, but noticeable at idle.
- Thread starter
- #38
No worries. My misfire is now a very faint occassional hiccup. Still have a few more things to address, but the biggest culprits were valves not set correctly when head was done first time, and there was a gouge on the on the intake manifold creating a vacuum leak / not sealing completely. Shop 2 had the intake manifold machined, and that’s corrected. Big improvement at idle, but from what I’ve seen and been told, they’ve all got a tiny hiccup every so often at idle.
In your case, you might want to have injectors serviced, check the intake tube between air box and throttle body- they dry rot and it may be on the under / backside of the tube, check the distributor cap and rotor, check the timing, look for vacuum leaks. Lots of places for vacuum leaks- from oil cap seal to brake booster (I had a vacuum leak at the booster, also).
In your case, you might want to have injectors serviced, check the intake tube between air box and throttle body- they dry rot and it may be on the under / backside of the tube, check the distributor cap and rotor, check the timing, look for vacuum leaks. Lots of places for vacuum leaks- from oil cap seal to brake booster (I had a vacuum leak at the booster, also).
alia176
SILVER Star
Might I suggest sticking a fuel press gauge into your system to rule out any fuel delivery anomalies? Be sure to get a 270 deg sweep, 0-60 psi (or close to that high end number) gauge so that you can really see any slight needle movements. Another Mudder replaced the fuel sock and stated his idle became more smooth. 
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I found a high # of vac leaks by using a buddy's smoke machine that pressurized my intake with smoke and compressed air. So, you may also have a vac leak during idling when the vac is at its highest. Worth looking into.
.I found a high # of vac leaks by using a buddy's smoke machine that pressurized my intake with smoke and compressed air. So, you may also have a vac leak during idling when the vac is at its highest. Worth looking into.
Thanks for that feedback. The small vac lines look pretty bad so I've ordered several feet of material. I'll also do a fuel press check and will probably have the injectors serviced. They haven't been touched and I can imagine they need some TLC.
