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Eric
Eric, Automotive Repair Shop Manager
Category: Honda
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Experience:  20+ yrs. experience as repair shop manager and technician.
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2001 Civic LX: you turn the ac off..idle rough..stop light

Resolved Question:

Hi, my daughters 2001 Civic LX idles roughly and almost shuts off when you turn the ac off. Just today she called me in a panic because the car idle rough, shook, and shut off at a stop light. Any help?
Submitted: 3 years ago.
Category: Honda
Expert:  Eric replied 3 years ago.
Hi,

is the check engine light on while this is happening? If so, has the computer been read for fault codes and what are they?

did this just start occurring, or was it happening as soon as you did the engine swap?

Customer: replied 3 years ago.
There is no check engine light on and it hasn't been on. This did not just start occuring. It was happening before the engine swap. Last night we were cleaning the car and I had my daughter turn the engine on and then turn the air off and on. It did not do it then....maybe because the computer was in open loop and the car wasn't warm?
Customer: replied 3 years ago.

There is no check engine light on and it hasn't been on. This did not just start occuring. It was happening before the engine swap. Last night we were cleaning the car and I had my daughter turn the engine on and then turn the air off and on. It did not do it then....maybe because the computer was in open loop and the car wasn't warm?

 

Also, I did notice that the car does not pick up the idle when the air is turned on. I thought that it should do that.

Expert:  Eric replied 3 years ago.
Hi,

i understand about it happening before the swap, but there are dozens and dozens of reasons for this, so it may or may not be related. a rough idle and shutting off are common for an engine with a cracked head.

so when you installed the new engine, on first test drive it was running rough and shaking, correct?

Is this an automatic or manual transmission?

on the engine swap, did you re-use all your sensors from the original engine, including distributor, crank sensor, engine coolant temp sensor?

did you verify on the new engine that all the vacuum hoses were in good condition and no leaks?

did you reuse your intake manifold and if so did you use a new intake gasket?
Customer: replied 3 years ago.

Oops I think I sent you the same message again. the first engine did the rough idle think before the head was cracked. She overheated it because a fan switch was bad. It occasionally just idle rough and felt like it was going to shut off. It also did it when the ac was turned off.

 

When the engine swap was done the engine did not idle rough and it ran fine. It does not idle rough now.....except on occasion when she stops at a light. She just pulled in the driveway and I went outside. When she turns the AC compressor off the idle drops way down and the car shakes...not quite stalling out.

 

the engine we swapped had all the sensors on it so we used them. We didn't swap the intake because the engine was complete. So, this thing is doing what it did before the swap. I haven't checked out the vacumm hoses. Should't it pick up the idle when the ac is turned on? Could it be the computer?

Expert:  Eric replied 3 years ago.
Hi,

possible that it is the computer, but no way to test it. Honda simply states "if PCM is suspected to be faulty, replace with known good one." considering their cost, we need to check some other things first.

i want you to check the vacuum hoses and intake gasket first. with engine idling, spray carb cleaner on each vacuum hose one at a time. If idle smooths out, then replace that hose. Next do the same for intake by spraying around the base of the intake manifold and if idle smooths out, replace the intake gasket.

IF ok, then we need to check the fuel pressure. A weak pump can cause this. idle should be 40-47psi. If under that, then replace the pump.

If these are ok, then we will go from there
Customer: replied 3 years ago.
I am headed out to my shop to check it out. back at you soon
Expert:  Eric replied 3 years ago.
Hi,

ok, let me know what you find and we will go from there
Customer: replied 3 years ago.

Found a code in the computer p1298 fuel air mixture

 

Also, what tells the computer that the ac compressor is on. It does not pick up the idle when the compressor is turned on. Does the switch on the dash that you push to turn on the ac compressor also tell the computer that the compressor is on?

 

No vacumm leaks and fuel pressure is good

Expert:  Eric replied 3 years ago.
Hi,

ok, this is actually for the ELD, electrical load detector, which will cause every symptom you have including it not picking up idle when ac is turned on. It is located in the fuse/relay box. There is a TSB(technical service bulletin on this. You will need to replace it to solve all the problems. this also explains why the problem occurred with old engine and new engine.

TSB(includes directions to replace). It is in pdf file format(adobe reader). Just click on blue highlighted word to open and download. labor time to replace is only 0.4 hours.

ELD DIRECTIONS

Eric, Automotive Repair Shop Manager
Category: Honda
Satisfied Customers: 25155
Experience: 20+ yrs. experience as repair shop manager and technician.
Eric and 2 other Honda Specialists are ready to help you
Customer: replied 3 years ago.

Thanks a bunch.......I will get the part tomorrow and see what happens. I'm assuming that I can do some kind of electrical check on the part to see if it is actually bad. So, the computer is not the culprit?

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