Little help please... Rough Idle, now lots of codes, I"m going crazy.

[DenverLX]

Hey guys, Im going crazy trying to figure out whats wrong with my truck. I have a 99' LX with 144,000 miles. About 4 weeks ago my car was idling very rough and then my CEL came on and I got P0171 & P0174, which is system running lean (vacuum leak?). I read tons of stuff here and thought it was either the mass air flow sensor or maybe the Throttle Body Sensor. I cleaned the throttle body and MAS, I check over the whole engine for vacuum leaks (did not find any) and I replaced the spark plugs and the fuel filter and air filter. The CEL never came on again and the truck ran much much better but now the engine was idling really high, between 1000-1500 depending on the day. I checked with Slee and another mechanic and both said that I its really hard to diagnose the problem without codes currently happening.

Yesterday my truck seemed to be idling a at 800 and very rough again, and in the afternoon I all the sudden had my CEL blinking like crazy. I also seem to have a loss of power, but could still drive fine, no noises or anything strange. I went straight to the auto store and had them run the codes. I had 9 codes!!!

P0153 Circuit for O2 sensor Bank 2 sensor 1
P0150 O2 sensor Bank 2 sensor 1
P0133 Circuit for O2 sensor Bank 1 sensor 1
P0130 O2 sensor bank 1 sensor 1
P0300 Random/multiple cylinder misfire
P0302 Cylinder 2 misfire
P0305 Cylinder 5 misfire
P0304 Cylinder 4 misfire

I have an ohm meter so I can test the coil packs today, thinking thats what it is but wouldn't just one coil pack go out at a time? Also I have a small exhaust leak, but I wouldn't think that would cause all this trouble. Maybe I need to replace MAS or TPS sensor? Im guessing my problem a month ago and this problem are related but the P0171 code did not come on this time. I also replaced 2 O2 sensors about 3 years ago, but i can't remember which ones I replaced.

Thanks for any help in advance, Ive dumped a ton of time and money into this truck in the last year, (timing belt, starter, water pump, tires, brakes, shocks) and Im getting really tired of spending my weekends in the garage and putting money into this thing so this recent problem is really irritating!

 

[Julian Stead]

Swap your coil packs around to see if the fault codes change. Sounds like coil packs, they do have multiple failures.

 

[SWUtah]

If you don't have a new Toyota/Lexus gas cap on your beast at that mileage get one. Also sounds like coil pack.

 

[Julian Stead]

Ps, this could be linked to P0171, as this means the engine is running lean, running lean means there is to much oxygen being read at the 02 sensors, a unburnt fuel mixture(misfire) in a cylinder will cause to much oxygen to be read by the 02 sensors.

 

[SWUtah]

Ps, this could be linked to P0171, as this means the engine is running lean, running lean means there is to much oxygen being read at the 02 sensors, a unburnt fuel mixture(misfire) in a cylinder will cause to much oxygen to be read by the 02 sensors.

Had that code when I replaced the gas cap it went away.

 

[abuck99]

^ copy that

 

[Julian Stead]

Had that code when I replaced the gas cap it went away.

Agree, this could be a issue due to air entering the fuel system from the tank. But I would just act on the fault codes presented by swapping coil packs. P0171 has multiple reasons to bring on the light and the cap is one of them.

 

[vipergrhd]

If money is not an issue just change all the coil packs they are just going to start falling apart anyway if you just replace a few,on the lean issue check the rubber intake tube for a split or crack where air could enter past the MAF. If you replace the coil reset the the computer and drive it till if any code returns and then fix it. Your upstream A/F sensor might be on it's way out also but i would wait until it return after changing your coils.

 

[SWUtah]

Agree, this could be a issue due to air entering the fuel system from the tank. But I would just act on the fault codes presented by swapping coil packs. P0171 has multiple reasons to bring on the light and the cap is one of them.

Cheap fix and everyone needs a new one after X years X miles and depending how hot/dry your area.

 

[abuck99]

I figured mine was due when I unscrewed it and the tank was pressurized

 

[Julian Stead]

I think a cap will be on my shopping list when I do my next oil change.

 

[bctlex]

I figured mine was due when I unscrewed it and the tank was pressurized

Is that a sign that the cap need to be replaced? Pretty sure mine does this too

 

[super90]

On the gas cap.....Just buy a new gas cap o-ring. That's what makes the seal. Everyone should do this on all their trucks because the are all of an age to need it.

 

[2000 LC]

I figured mine was due when I unscrewed it and the tank was pressurized

I thought this is how you know your gas cap is still working.

If there's no pressure then the seal isn't holding correct?

I've got 16 years 200k on my gas cap...

 

[PADDO]

Yes, the cap is suppose to hold a slight positive pressure - if it's not then you need to replace the outer visible gasket or the spring loaded vacuum seal within the cap isn't sealing properly. A new cap solves both potential leakage points.