Very difficult cold starts, rough idle, dies under hard throttle. What could it be?

[LawFromTekken]

Hi guys!

I have some trouble with an 1986 Accord EXi. When it's cold it's nearly impossible to start, but it starts fine when using a block heater. It also has rough idle, and dies when I press the throttle unless I do it VERY slowly, in which case it revs fine across the register.

Things I've replaced:

Ignition coil
Fuel pump
Fuel filter
Air filter
Alternator
TW sensor

I get no error codes, except when I tried unplugging the TW sensor to see if the connector was broken. Then the warning light came on after about a minute. Code 6 remained after I plugged the connector back in, so I unplugged the battery to reset the codes. I tried starting it again after a couple of hours, and it fired right up! It then went through what I assume is the normal sequence of elevated revs from 1500 down to 8-900 for maybe five seconds. Also had perfect throttle response, and no stalling even after doing a crawling start only using idle.

That was yesterday night, and I got the same perfect result when I tried starting it again today. Excited, I loaded her up with things to take a long test drive. Then when I was about to set off, all the old symptoms came back. Cranking for several minutes (with pauses), barely any idle, have to be very gentle with the throttle, while at the same time keeping the revs high so it won't die when coming to a stop.

Anyone know what I should try next? It's my father in law's car, and right now he has to share a car with his wife

[conozo]

Can you verify its getting spark when its cranking and not starting?

You can use one of those inline spark plug testers where you can see the spark. Or if you have a timing light, you can use that as well.

Also make sure your coolant is bled and have all the air out of the system.

[LawFromTekken]

I can confirm it's got spark when cranking. I got him new plugs last year, and he's since driven about a 1000 miles. Now they look like this:



It's suddenly gotten 15 degrees warmer outside here, so now it only takes 10-15 seconds of cranking before it starts. But it still randomly dies when idling, and bogs down when I push the throttle, unless I do it incredibly gently. Full throttle only works above 5000rpm.

Outside of checking spark and coolant level today, I also tried polishing the points in the distributor cap and checked the tps. It read 0.5-4.5V between closed and fully open. Do you know of anything else that could cause something like this? I almost wish it had a carburetor at this point

[LawFromTekken]

I did some vacuum leak tests with starting fluid today. No luck. It also died when I sprayed directly into the intake. Not sure if that's a clue, or just what normally would happen

[Oldblueaccord]

Those plugs are dead rich.

You sure the TW sensor is correct and no codes?

The TW sensor goes bad the car will be very very rich on start. I did a video and put it on the EFI forums about diagnosing the TW sensor.

[LawFromTekken]

Those plugs are dead rich.

Yeah, that's what's throwing me off. I'd guess that the engine was running lean since it won't start at all when it's cold, like today. But then the plugs look like this...

You sure the TW sensor is correct and no codes?

The TW sensor goes bad the car will be very very rich on start. I did a video and put it on the EFI forums about diagnosing the TW sensor.

Yeah, no codes

I couldn't find the video, but I took the sensor out today and tested it along with the old one in a pot of water like test in the "master manual". Both were within .5kΩ of each other, so I probably didn't need to buy the new one:

2.89kΩ at 7°C
1.04kΩ at 50°C
0.48kΩ at 75°C

I recorded a video of how it acts when it's cold outside:
https://www.youtube.com/watch?v=QcZiy0w5_MA

[Oldblueaccord]

https://www.3geez.com/forum/showthre...-Clarification

Im not sure what the correct setting are off the top of my head EDIT: the sensor specs are listed in the link above, but there is a paper clip bypass that should prove out its the sensor. The "no start" is from way way to rich usually.

[LawFromTekken]

https://www.3geez.com/forum/showthre...-Clarification

Im not sure what the correct setting are off the top of my head EDIT: the sensor specs are listed in the link above,

Thank you! That nifty air/fuel mixture meter sure would've come in handy The car wouldn't start at all today despite it being 25°C/77°F outside, and
the paper clip bypass sadly made no difference. So I plugged in the block heater for 30 minutes, and she fired right up. I let her idle for 15 minutes and recorded this, to show the throttle response:

https://www.youtube.com/watch?v=5Rg7c6h6LQQ

I then took her out for a couple of hard 0-60s and drove around for a bit. That eliminated basically all of the problems, except the engine still hesitates and even cuts out at wide-open throttle and low RPM. (30mph at 2000rpm). At this point, using the gas pedal when idling feels like it should:

https://www.youtube.com/watch?v=Mdly4mrawhA
(I didn't reset the code between trying the paper clip at different times)

Finally I measured the sensor, which showed 200Ω like it should, and 5V between the yellow/green wire and ground.

It says to replace the ECU if the sensor passes the test. Is that really the next step, or is there a way to check its functionality somehow? Or is there something else that could cause this behavior?

[Oldblueaccord]

Im USA but my car was made in Japan and its built 1987 listed as a 1988. When I turn the key on I see the off yellow PGMI light come on on the dash. I dont see it on yours but im not sure if thats a ECU issue or your car is EU spec.

I would unhook the the TW sensor, start it and see if you get a code on the ECU and a check engine light on the dash. Thats be a good check.

New spark plugs also. NGK like the hood stickers says the base copper ones nothing fancy.

[LawFromTekken]

Im USA but my car was made in Japan and its built 1987 listed as a 1988. When I turn the key on I see the off yellow PGMI light come on on the dash. I dont see it on yours but im not sure if thats a ECU issue or your car is EU spec.

The light does come on, but only when the fuel pump is priming:

I would unhook the the TW sensor, start it and see if you get a code on the ECU and a check engine light on the dash. Thats be a good check.

I tried unhooking the TW sensor while the car was idling, and it sputtered and almost died before recovering. The ECU showed code 6, but no PGM FI light. I plugged it in and out a couple of times, resetting the battery and tested with a paper clip, with the engine off or on, etc. I got the code every time the sensor wasn't plugged in, but never the light on the dash.

Would that be indicative of a bad ECU? I hope not because the only one I can find in Sweden is a used one with 250,000 miles on it for $85

New spark plugs also. NGK like the hood stickers says the base copper ones nothing fancy.

The once I got last year were BPR5E, without the S or Y. Is it worth trying a colder plug this time?

[Oldblueaccord]

Im have run 5's I think 6's are better. Correctly gapped. Nothing wild.

Drive it some also, bad or old gas doesnt help.