3.4 won’t start when warm

Hey guys so recently my truck (owned for only a few months) will not start when warm. It starts on cold mornings and it will stay running but if I drive for say 20 minutes then turn it off it will not start. After sitting for 15-20 minutes it will start again.

I tried unplugging the MAF then starting with no noticeable change. This was while I was still collecting data so I tried a few minutes later with the MAF still unplugged and it started! I plugged the MAF while it was running then and it died.

Later that day I could not get it started again and it didn’t seem to matter if the MAF was plugged in or not.

I’ve read this could be a coolant temp sensor issue, MAF issue, or IAC issue. I’ll start cleaning what I can of the intake side but thought I’d check in here first.

Items I've replaced:

PCV, grommet, and hose (oem)
Vacuum hoses (evil energy)
Purge valve, driver side engine bay (oem)
O2 sensor, downstream (oem)
Coolant temp sensor, under timing belt cover (oem)
Gas cap (oem)
MAF, (replaced no name with used oem)

NEXT: valve cover gaskets, throttle body gaskets, injector replacement


ALSO while looking over the engine bay it looks like a vacuum line on top of the manifold is missing hoses?! I can’t find where they would go though. Is it supposed to be like that?

 

Seems like you're in the ballpark of where the issue lies. That tube connected downward at a 90 deg angle to the IAC valve

 

My first choice would be leaking injectors fouling the plugs .

Plugs dry off it starts .

Always starts cold?

 

Coolant temp sensor would pop a code sometimes; do you have any codes?

It would also smell like fuel since your vehicle would be running rich as it 'tries to warm up', not to mention a higher than normal idle.

If these are not your symptoms, then aim at your MAF or IAC first.

 

I have same issue and end up changing fuel pump, strainer and fuel filter. Don't forget to clean fuel tank inside. Problem solve.

 

The back side of that metal vacuum line should have another hose connecting to the fuel pressure regulator that sits behind the manifolds there. Like this. It’s a very short distance. On mine it’s that small black hose that bends down.

 

I did look at codes but most are related to me driving with the MAF unplugged. I found a very loose vacuum hose under the foam cover of the PCV hose.

I have some new parts coming:

- evil energy 3mm, 6mm, 8mm silicone vacuum hoses
- PCV and grommet
- fuel filter
- wipers
- MAF cleaner

I’ll update once I get these in!

 

So it’s been a hot minute since I last posted. I installed the new PCV and grommet, fuel filter, vacuum hoses, and wipers but the no start when warm still persisted.

I wanted to test my fuel pressure but there doesn’t seem to be a schrader valve to test with.

I moved onto my hunch which was the coolant temp sensor and also an oxygen sensor since I’m not sure if the original is still in there.

So I popped the CTS coolant temp sensor in and presto! It’s started every time since then. I will say there are some stumbly starts but not like before.

I’d throw my oxygen sensor in there but it looks like the original one is deeply rusted in there. I see a trip to the exhaust shop in my future.

Now today I got hit with a CEL and 5 codes related to my purge valve so I’ll get to working on that next.

 

FUEL PUMP see my post below

 

Total shot in the dark and probably useless info, but I had a motorcycle years ago that had this same issue and it was either bad ignition coils or bad spark plug caps? This was ages ago and I can’t remember which it was but the heat was causing something to expand and separate, and when it cooled it was fine. Idk. Maybe ignition stuff like that is worth checking!

 

Another delayed update!

Well I did get my rear O2 sensor installed at the exhaust shop. They fixed a few rusted joints and a hole near the muffler which quieted everything down quite nicely.

I also replaced the purge valve located in the driver side engine bay. I bought an aftermarket one from Rockauto and it turned out to be a Toyota original!

Now after quite some time the no-start-when warm has come back along with the same purge valve codes. I read there are 2 other purge valves that could be the culprit. I picked up a smoke machine from Amazon so once I get some mineral oil I will do a smoke test and see if there is something I'm not seeing. I know my valve cover gaskets need replacing. I have them, but I need to make some time.

I also purchased an OEM gas cap as the original was quite cracked but didn't seem to make a difference.

 

Well yesterday I had another no start issue after driving to Home Depot. I had driven to my first stop, parked then started up and drove to HD, where after parking and shopping for 15 min. came back and started it up. It ran for about 2 seconds and then stumbled off. Then it wouldn't start anytime after for about 20 min. I then started it with the pedal to the floor and had to feather the pedal to get it to run all the while popping and misfiring. Threw it into drive and got it back up running. I did start noticing it was low on power on slight acceleration from a stop light, which I then just accelerated faster and it seemed to disappear. Also....no CEL

On to the next suspicious item. I found that the MAF had been replaced by a PO with a no name brand so I have an used OEM unit on the way.

 

Did you get the issue fixed and if so what corrected the problem? I have a 2001 that is doing the same thing. Any advice would be helpful

 

I hate when ya have to just start throwing parts at a problem, I’ve heard multiple trucks with this same issue and have yet to hear a solution to the problem

 

Well, what was just a MAF replacement turned into look my alternator belt is worn, then oh my other belts are cracked, then well, might as well do the valve cover gaskets, they are leaking, then we’ll I’m pretty deep in here, let’s do the injectors...and I’ll just pull all these rusted and corroded brackets and wire wheel and paint them

Glad I pulled the trigger on new injectors because each and every one of the originals practically fell out of the fuel rail and had cracks in the housing. I have a new set of Motorwest denso’s coming!

 

Wow someone was in here before and used a lot of gasket sealant! I’m guessing they didn’t want to buy new valve cover gaskets.

 

Might have been this needs up and running no time to wait for gaskets. I know I have been there all to often.

It worked so no reason to pull things apart to change something that was working.

 

So I’m all back together after new valve cover gaskets, manifold gaskets, belts, and Motorwest Denso injectors. I also put in a used Toyota MAF instead of the non name one that came with the truck.

I am here in the Lowe’s parking lot again (after a short 15min drive with 3 stops) and we’re not starting. So it’s not the injectors!

I do have a P0171 code coming up now so I’ll be diving into that, also a new ABS light flashing only when stopped.

Good Lord.

 

Replace your fuel pump.

 

Just looking at some of the pictures of your engine bay- have you checked the gounds and cables? Cables can corrode from the inside out, and the grounds can have poor contact.

Also, with your ABS light- be careful when coming to a complete stop. If the ABS kicks in, and it feels like you can't stop, ya gotta take the transmission outta gear (manual, push the clutch in, auto shift to "N") and be ready on the e-brake.