Chasing Check Engine Lights [RESOLVED]

I recently bought an 02 Tacoma 2.7L 4 cylinder with a blown head gasket. Did a complete rebuild. Restored cylinder head, replaced belts, pumps, timing chain etc. Have worked through a bit of tuning issues from misfires to fuel leaks. Now everything is buttoned up and running, but I’m getting check engine prompts related to the intake system. Checked the hoses with starter fluid spray, cleaned the MAF & throttle body, replaced the IAC, even dialed in the idle set screw to get it in a happy idle zone. Today my check engine came back on and it’s 4 codes all saying my air flow system is whack. I’m at my wits end…anything I could be missing? Thought about doing a professional vacuum leak test at the mechanic but obviously curious what others have ran into.

 

What are the code numbers you are getting?

 

Check for vacuum leaks with a unlit propane torch or starting fluid.
The idle RPM will increase if there is a leak.

 

we are going to need the codes that are present and the pending ones if there are any in order to help. In adition, is the engine 100% stock, no C.A.I. or headers or modified anything?

 

The engine is stock with exception to after market parts I’ve installed. Codes I have currently are P0110, P0100, P0505, and P0401. I had a smoke test done today to check for vacuum leaks and that was a dead end. Zero leaks. Even the mechanic was unsure of what my issue was. The brake pedal is sluggish the first half of pressing and the stiff for the remainder, they work but maybe a bad booster causing issue with vacuum?Power steering is a little stiffer than I’d expect, even after correcting fluid levels and changing the belt. Discovered today the exhaust pipe vibrates heavily when at a stop light. Noticed by partner as she followed me from one place to the next. Let me know if there is more I can answer. I’ll gladly take videos if that’s helpful and try whatever tricks y’all have in mind.

 

what do the plugs look like

compression all 4 cylinder notated

 

Plugs are clean. As for compression all I know is the professional who rebuilt the cylinder head confirmed everything was within spec.

 

P0100 and 110 are circuit codes for the MAF and the Intake Air Temp Sensor which are combined into one unit so you need to inspect the wiring and connections first.
P0401 is insufficient EGR flow, you will have to verify that all the EGR system is hooked up correctly and functioning.
P0505 is a problem with the Idle Control System, since you say your brake pedal is stiff I'd cap off the vacuum line going to the booster first and see if it runs better.

 

I have a new MAF arriving tomorrow, so I’ll replace that and inspect wires. Ill test the brake booster, look over the EGR system and clean the EGR valve as the throttle body was pretty dirty. I’ll keep everyone posted as I move forward.

 

Interesting add on. I picked the truck up from where I was storing for the night and noticed Only when the ac was running through the vent. Not recirculating, I got a faint fuel smell. Went away when I turned it off and ran the vent. I’ve checked the fuel filter three times the last few days and the fuel pump connector, no leaks. Could this be excessive fuel being added into the engine?

 

Update: Replaced the MAF, Tested the EGR vsv, modulator and valve. All is good. Fuel injector had a bad O-ring that finally failed enough to leak fuel. Replaced that ASAP. Brake booster passed operation and holds air pressure. Fuel injector was definitely the sad engine cause and the check engine lights are gone, maybe the MAF was the cause. I only have a rough idle now when the ac is on and brake applied. No ac and brake, all good. AC and in park, all good. Rough idle is last if it’s trying to stall. Drops and fluctuates between 500/650 (roughly) until I turn the ac off or let go of the brake.

 

the 4 cylinders are notorious for a rough idle especially when there is a load on them. I solved my issue by replace the throttle body on my 03 - 2.4 MT so I didn't get a chance to play with "things"... what I was going to do if replacing the TB didn't solve my problem was I was going to measure the TPS readings and loosen the base idle adjustment screw and see if I could get 75 rpms more w/o a change in the TPS reading... there is a little slop. While the TPS is not "adjustable" I see where I could elongate the screw hole slots for some additional tweaking. Should you have to do all of this, hell no, but Toyota wasn't expecting these trucks to be on the road for decades so tweaks have to be introduced... not everyone wants to put a $300 + TB on a 20 year old truck. Will this work... I dont know why not, they only caveat I can think of is if the base idle is too high the PCM will try to adjust the idle by altering the IAC dwell and if the PCM isnt getting the feedback that it is expecting, that just might trip a code.

 

Idk, my truck is a 3.4. The one thing that I read that stood out was the sluggish brake pedal. Adjust your rear brake shoes up and see if that goes away. Out of adjustment rear shoes will cause a long travel brake pedal feel, sluggish at first, then gets firm.

 

Soooo I decided to swap the O2 sensors just for piece of mind down the road…and boy am I happy I took a deeper look! I don’t know how this didn’t trip my check engine light! Engine has a nice balance to it now.



The ac is still giving me trouble so I’ll take the control panel out and check that for faulty wires and follow back in the engine bay. For now I’m happy to ride without ac. Brakes have improved, smoother engine for the power booster maybe…?

 

Wow! Nice catch.

 

Guess what…truck is acting up again and now I have a p0402 which is telling me I have too much exhaust going in. Could it be a faulty EGR valve or something else? I tested it and verified it operates but maybe it’s not operating correctly? I have “Not Ready” on my I/M scanner for CAT, HCAT, EGR, O2S and another I can’t recall but it all points at my exhaust. Any areas I could test before swapping EGR valve?

 

P0402 is bad catalytic converter or a bad 2nd o2 sensor...

 

Your thinking of P0420/430, P0402 is excessive EGR Flow.
First thing to check is if the EGR temp sensor is reading correctly.

 

Lol... my bad. I had the same issue with my truck when I got it, one new EGR temp sensor later and the code was gone!

 

Thanks! I’ll give it a test. Supposed to rain the next few days so it may be bit before I get to testing it