A friend's 2011 Accord, 2.4L, AT is presenting quite a challenge

The car has about 215,000 miles and was well cared for. It currently presents two drivability problems, two error codes, and has poor gas mileage according to her son. These problems have been going on for months.

  1. No start when hot - intermittent, happens most of the time.
  2. High and fluctuating idle from cold start to fully warmed up- 1,100-1,500 rpm
  3. P0171
  4. P0507

The following was done to deal with these conditions in order of first to last, more or less:

  1. New O2 sensor, installed by a local shop - no effect (this is where I got involved)
  2. New coolant temp sensor installed to correct ‘no start when hot’. Idle relearn procedure done - no effect
  3. Vacuum hoses checked for leaks visually, and aurally with hose, to address P0171 - none found
  4. MAF sensor cleaned with CRC MAF cleaner, and air filter changed to address P0171 - no effect
  5. Checked voltage to MAF sensor - OK. New MAF installed - no effect
  6. Lucas Oil fuel treatment added to gas tank to address the possibility of leaking or clogged injectors.
  7. New throttle body installed with integral TPS and IAC valve (they can’t be purchased separately) to address ‘high and fluctuating idle’ - no effect
  8. Checked coolant level to ensure no possible air bubbles keeping coolant temp sensor from accurately reporting temperature. Checked coolant temperature with infrared thermometer with radiator cap off about 15-20 minutes after engine shut down - reading of 165F. Seemed to indicate correct temperature reached when engine fully warmed up, but will check more accurately later.
  9. Checked manifold vacuum at idle of 1,100rpm - 20 inches
  10. Replaced defective PVC valve - no effect

My friend just received her CA DMV registration renewal notice and needs to have the car smogged, so 6 to 8 weeks to solve the problem. My next plan of action is to unplug and replug the connectors to the ECM in an attempt to freshen up the connections, and check the fuel pressure, and keep searching the net for answers. I am reading posts here dealing with P0171, P0507 and ‘no start when hot’.

These obviously can’t happen at the same time. If there’s a no start, then there is no idle, so it can’t be high and fluctuating.

So when is the high and fluctuating idle? Only on cold start? Or also when all warmed up and still running. (But then if shut down hot it won’t restart?) IDK.

No starts when hot, coupled with wonky idle always make me think of the fuel system not holding pressure on shut-down. If you have a fuel pressure gauge, slap it on there and look at what’s happening both while it’s running and on a hot shut-down.

Another thought is that the no-start hot is an ignition issue and the wonky idle is
well, any number of other things but vacuum leaks (P0171) do come to mind. Visual and aural checks can only take you so far. Maybe carefully feed something flammable around the intake and other vacuum connections looking for a reaction. I’ve sometimes used an unlit butane torch with a pc of rubber hose attached. It works. Just don’t light it first.

Thanks for the suggestions. The high and fluctuating idle is from the time the engine is started cold to the time the engine is shut down either cold or hot. The engine will start only after it has cooled to a certain point, but it does not have to be fully cooled. It seems that between 20 and 40 minutes after shut down the engine will start again. It varies. I should edit the original post to read that this condition is intermittent, meaning it will sometimes start when hot.

A fuel pressure test and either a smoke test or propane torch to test for vacuum leaks is definitely in order. I will keep a fire extinguisher handy. for the latter.

That sounds like vacuum leak. Don’t overlook the intake manifold as opposed to just the vac hoses.

And that sounds like a fuel system/pump not holding pressure. If it doesn’t hold pressure, the fuel in the lines can vaporize and shoot fumes instead of liquid fuel. (Sort of like the old problem of vapor lock). One simple way to check is to prime it up before starting - turn the key to the run position (without cranking) and back off a few times, and then crank it. Each time the key goes to run it runs the pump for a couple/few seconds. Cycling it a few times pumps up the fuel pressure.

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Before doing any other work on an engine with over 200K,do a compression test to see if it is worth fixing.

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Yes, that was in the back of my mind. I am surprised at how easy it is to remove a plastic intake manifold versus old metal ones. Will definitely check it out.

I suggested this to the owner early on. They reported having tried it, but no success. I wish she would leave the car with me for a few days, it would make it easier.

Thanks, will give it a shot. It’s an inline four so pretty simple.

and what do you intend to do?

smoke it?

Hook up a fuel pressure gauge?

Fuel pressure gauge for sure. I may smoke it after checking the manifold bolts for proper torque.

My friend reported her most recent experience after the last no hot start:

Yes! I was there till 5pm. The car wasn’t starting but I tried giving it a little gas when it was trying to die, and it finally started. I stopped at 2 traffic lights. When the light turned green, I drove the car and after crossing the intersection and reaching 3000 rpms, car momentarily seemed to lose power and jerked, but overcame whatever the problem was, and drove fine. Then, second incident occurred after I stopped at next traffic light and then continued driving; again rpms were 3000 and the same problem occurred, but less intensity. We’ll, let’s not lose sleep over it. Enjoy your Sunday and we can talk about it next week.

I will smoke it tomorrow with a DIY smoke machine involving sticks of incense soaked in baby oil, an old fashion tire pump and some 1/4 inch ID vinyl tubing. I will try to post a picture of the final product in action. After that I will pressure test the fuel system, either with a pressure meter I have on hand and some hoses and clamps, or a loaner from the local chain autoparts store.

Performed a smoke test and a fuel pressure test on this vehicle today. The smoke test revealed no leaks. When I pulled a vacuum hose during the test smoke came pouring out, so I know it was working.

The fuel pressure test revealed that the fuel pressure at the rail was very low: 32psi. The Haynes manual says between 48 and 55psi for the four cylinder.

So now I am wondering if a relay with corroded contacts might be the cause for low fuel pressure, and is it worth throwing a new relay at it before committing to changing the fuel pump assembly
 When I pulled the relay after the test it seemed warm, which could indicate high resistance through the contacts.

The fuel pump is weak and needs replacing

Tester

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Thanks, tester. Is it possible that the fuel pump relay is at fault?

No. The fuel pump relay allowed the fuel pump to run the 1-2 seconds to build the proper fuel pressure. But the weak fuel pump couldn’t.

Tester

Is it possible that the relay is consuming some the voltage meant for the pump due to corroded contacts? That would be analogous wires of a smaller gauge powering the pump. As a carpenter I can recall running a Skilsaw with a 50 foot, 16 gauge cord from necessity, and recall that it ran weaker than with the usual 14 gauge cord.

The vehicle needs a new fuel pump. Comprende?

Tester

Nah, I don’t understand you at all.

No. The relay is not the cause. But if it makes you feel any better, find another identical relay in the box that is non-essential. (E.g. sometimes something like the A/C system uses the same relay as the fuel pump). Swap the relays and see if there’s a change. (There won’t be). Or, heck. Relays are pretty cheap. Throw in a new one. When the results are the same, replace the fuel pump.

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Found this:

When discussing electrical relays, “contact resistance change” refers to the variation in electrical resistance that occurs between the relay’s contact points over time, primarily due to factors like wear and tear, environmental conditions, and the load being switched, causing the resistance to increase and potentially impacting the circuit’s functionality; essentially, the contact points become less conductive as they age.

However, the relay in this case may be a solid state relay, and I am not sure if or how they degrade over time, but did find this:

The semiconductor elements within an SSR can degrade over time due to prolonged exposure to thermal and electrical stress, leading to wear-out and failure. This degradation is often gradual, resulting in a decline in performance before complete failure.

Also found this:

Key failure mechanisms within an SSR:
Electrode wear:
Repeated switching operations can wear down the electrodes within the thyristor or triac, increasing on-state resistance and generating excessive heat.