I just got a 1990 CRX DX 1.5L and it idles at a constant 3k. I have drove it around 50 miles to get it warmed up and see if the idle would go down, it didn't. I checked the codes and it had...

Oxygen Sensor "A" (Primary)
defective circuit or unplugged / defective sensor

IAT Sensor (Intake Air Temperature)
defective circuit or unplugged / defective sensor

TDC Sensor (Top Dead Center)
defective circuit or unplugged / defective sensor

IAC Valve (Idle Air Control)
defective circuit or unplugged / defective sensor

I replaced the Oxygen Sensor "A" last night and it didn't seem to help. I disconnected the battery and no codes will flash. I will take it out for another drive today to see if I can get a code to flash.

If I push up on the throttle dishpot diaphragm assy (part number 16044-PM5-A01) it will idle normally but as soon as I take my finger off of it, the idle will go back up.

I am not a mechanic and I am new with hondas, any help would be appreciated.

Thanks!

 

Most likely the dashpot is causing a big vacuum leak. A lot of people just cap all the ports off and leave them unhooked. Either way you should figure out the rest of the codes as well. Don't let it keep idleing that high (especially sitting still with no engine load). Before you know it you will have "knocking rods" saying "hello".

 

N3va3vaSatisfi3d, thanks for the advice. Do you know how I should bypass the dashpot? I just took it out again, hasn't thrown a code in 20 miles. Still revs at 3k.

 

Last night I replaced the oil, tranny fluid, CV joint and cleaned the high idle control unit. None of it seemed to help.

I think tonight I am going to flush the cooling system. Last night it would bounce between 1500-2000 rpm repeatedly. But today it just stays at 3000 rpm. I remember once before when it was bouncing back and forth like that it was low on coolant. But the coolant is topped off. The temperature gauge works and it seems to be heating up fine and not overheating.

I also tried to bypass the dishpot and just plug the vacuum lines. That didn't help at all. Any other suggestions?

 

Have you bled the coolant? Air bubbles could cause the IACV to act up. Also, have you checked out the FITV (Fast Idle Thermo-Valve)? It is below the throttle body and it is a mechanical IACV... when the coolant heats up to a certain temperature it is supposed to close and the IACV will take over.

If you pull of the back cover (2 small bolts) there will be a ceramic piece in there. Turn that most of the way in (you will see when you pull off the cover that it might be all the way towards the cover if this is the problem). Basically that part gets stuck open and makes the engine have a huge vacuum leak.

Another thing could be your brake booster leaking. Start the car and pinch off the vacuum line for the brake booster. If you idle goes down you have a bad brake booster.

A bad TPS ground could also cause this symptom. I can't remember what cars it was for but there is a FSB (Factory Service Bulletin) out on it.

Finally do you still have the codes? I would really look into those as well.

 

I no longer have any codes. Do you have a picture of where the FITV is located? I thought this is what I took off and cleaned but it didn't have the ceramic piece your talking about in it. This is also on the D15B2 motor (not sure if that helps). I will check the brake booster tonight! I checked to see if the coolant was full and it was, but I am going to flush the coolant tonight and bleed the system. Again thanks for all your help!

 

OH... LMFAO... The FITV is for MPFI... you have a DPFI... Whoops... Oh well.

 

Another thing to check maybe is the Coolant Temperature Switch. That can lead to a higher idle. I would check the voltage at the TPS as well, it should be around .5v closed and about 4.8v WOT.

Here is the FSB you can look at, your car is probably included.

91honda04

Bulletin No.
91-031

Issue Date
NOV. 1, 1991

File Under
ENGINE

Model

'89-91
CIVIC

Applicable To
SEE VEHICLES
AFFECTED

Occasional Rough Idle

SYMPTOM

1. The engine may occasionally idle roughly or erratically after coming to a stop with the throttle fully-closed.

2. The engine may have a high idle upon start up or after it has reached operating temperature.

3. On 1990-91 cars equipped with automatic transmission: Even though the proper procedure is followed, the shift interlock system may occasionally prevent the driver from shifting out of Park.


VEHICLES AFFECTED

All 1988-91 Civic models equipped with 1.5 liter engine and dual-point injection, thru VIN:

1HGED3...ML011574 (Sedan)
2HGED6...MH512869 (Hatchback)
JHMED3...MS031565 (Sedan)
JHMED8...MS012826 (CRX DX)
JHMEE2...MS004778 (2WD Wagon)

PROBABLE CAUSE

Inadequate grounding of the throttle angle sensor circuit.

CORRECTIVE ACTION

Replace the existing ground wire with the new ground harness listed under PARTS INFORMATION.

1. Disconnect the three-pin connector from the throttle angle sensor.

2. Remove the GRN/WHT wire from the three-pin connector with Pin Tool E, T/N 07JAZ-002050A, from the Terminal Pin Repair Kit (see TOOL INFORMATION).








3. Cut off the GRN/WHT wire as close as possible to the gray tape wrapping the wire harness. Discard the cut off piece.

4. Install the terminal end of the new ground harness into the three-pin connector. Gently pull on the wire to insure the pin is securely locked in the connector.








5. Route the new harness under the existing harness. Hold the harnesses together by wrapping them with 3M 33+ high-temperature electrical tape or equivalent. Wrap the tape as shown, making sure it completely covers the gray tape and any exposed end of the GRN/WHT wire.








6. Remove the bolt holding the harness bracket to the intake manifold. Install the eyelet on the new harness between the bracket and the manifold and reinstall the bolt.

NOTE: The harness eyelet must be installed as explained above. If it is installed between the bolt head and the bracket, the symptoms may not be corrected.


7. Reconnect the three-pin connector to the throttle angle sensor.

8. Test drive the car. Verify that it idles smoothly and at the proper speed.


PARTS INFORMATION

Grounding Harness: P/N 32105-PM5-315
H/C 3976487


TOOL INFORMATION

Terminal Pin Repair Kit: T/N 07JAZ-003000A
H/C 3087707


WARRANTY CLAIM INFORMATION

In warranty: The normal warranty applies.


Out-of-warranty: Any repair performed after warranty expiration may be eligible for goodwill consideration by the District Service Manager. You must request consideration, and get the DSM's decision, before starting work.

Operation number: 121168

Flat rate time: 0.3 hour

Failed part: P/N 32105-PM5-315
H/C 3976487

Defect code: 066

Contention code: C99




P.S Please be certain if there are any codes present.

 

beat me to it - the D15B2 doesn't have FITV - sounds to me like your problem is with the dashpot - if it were working normally and you disconnected the vacuum line to the dashpot, the idle should go up to about 2500rpm +or- 500 - since idle doesn't change when you disconnect the vacuum line and you can get it to idle correctly by closing the dashpot, either the vacuum line to the dashpot is leaking or the dashpot diaphragm is shot and not holding vacuum

 

Yeah, this whole time I have been going at it like a MPFI. Oh well, almost everything is the same anyways (when it comes to trouble shooting). The dashpot on a DPFI actually cracks the throttle open to help start the car. When the vacuum is seen after the motor starts the dashpot lifts off the pressure on the throttle blade. If you want to get rid of the dashpot you have to just take it off on a DPFI. On a MPFI you would just cap off all of the vacuum ports.

Sorry for that confusion, it is my fault for not reading right. Take off the two screws holding he dashpot on. Then pop off the rod. If you idle is good then that was the problem all along. For better starts with the DPFI garbage system, then replace the dashpot.

 

Thanks so much everyone! I took the part off this weekend, and plugged the vacuum line. It runs perfectly. Later on down the road I might replace the part. But its $255 from the local dealership here. Anyone know of any good shops to get replacement parts from on the internet?

Again, Thanks so much!

 

I've got the same problem. I can close that dash pot manually to reduce the idle. I was working perfectly this week after I fixed my eacv wiring, but today it's got to be idling at 3k after the drive to work. I pulled the vacuum line and the idle went up a little bit. It's too bad that ill have to remove this, because I've had to hold the throttle down a little to get it to run on cold starts the whole time I've had the car unless its warm outside.

 

The dashpot is designed to delay sudden closing of the throttle plate when you open and then release the throttle. It keeps the throttle slightly cracked opened and then slowly releases it to fully closed idle position. It uses engine vacuum to assist its function. The vacuum signal varies depending on engine speed and throttle open/closed.

I'm guessing you probably fixed it by now since you haven't posted back but for simple troubleshooting, when its running fast idle like 3k try pulling the IACV connector off and see if it idles down to 1k or less. If it does then probably the IACV is sticking. If it keeps idling fast, you have alot of air getting into the intake somewhere, major vacuum leak or possibly your FITV (Fast Idle Thermo Valve is sticking open or is loose adjusted)

Let us know if you found the cause.

Thanks

 

I did fix the problem. I removed the dash pot and disassembled it. It had a small hole in the diaphragm which caused a vacuum leak. So I left it off, then I ran wires from the EACV plug to the ecu and it fixed the rest of my startup problems where it wouldn't idle without my help on a cold start. It's all good now except for an occasional high idle after I've been driving for a bit. If I blip the rpm up 500 or so it goes back down. Not a big deal but just another annoyance. Running well otherwise.

 

I had a problem of high idle. I cleaned the IAVC and it didn't work, still high idle. I took apart the vacuum dashpot and their was 2 pin holes. So I used liquid tape to fill the holes and now it idles correctly. so if you have high idle check the vacuum dashpot for holes before you do anything else

 

That's the one attached to the butterfly, right? I removed that altogether a while back and then it idled normally, but would sometimes go very low. not to the point of stalling, but would cause an annoying vibration/rattle. So, I picked up another one at a junkyard and installed it. not I get a fluctuating idle and after its warmed up, if I stop at a store and start the car up to leave, it wants to idle around 2500+. Sometimes a good rev will make it drop back down. But I suspect this one has developed holes in the diaphragm also. (My old one had one)

 

I am pulling mine off today, and this sounds probable to what is causing my issue. What is this "liquid tape"?

 

It is just liquid electrical tape. Comes in a jar with application brush. Can be found at most parts stores, electrical supply stores, and even WalMart usually carries it. You can also use any type of sealer / glue designed for rubber use.