CRX Engine RPM "Hunting" problem

[101mpg]

'89 CRX DX 1.5, normally about 42 MPG.

A month ago when starting, the engine would "hunt" for the right idle RPM until warm.

This past week: if I step on the gas any more than a TEEEEEENY bit, the RPMs will drop about 1000, the engine is getting NO gas for about a second to a second and a half. Then, it ROARS to life at the speed that it should.

Driving and letting off the accelerator as normal - this condition continues. "Stomping" on the gas will create the issue as well, EVERY time.

Changed fuel filter - no difference in vehcle's performance.

It now "hunts" for the right RPM most of the time. 129,000 miles, new distributor, new fuel filter, brand new plugs, brand new wires, etc. Otherwise runs just fine.

Any help is welcomed.

[dkjones96]

Sounds like TPS. The lower throttle positions around idle tend to be used the most often and that's usually where it fails.

[101mpg]

I've had the throttle position sensor checked and it is fine.

I DID have a new timing belt and water pump (badly needed) installed yesterday. Expensive, but good preventative maintenance. Situation improved SOME. Problem still exists, but just not as bad.

The fuel sending unit (fuel pump and fuel gauge sender) needs to be replaced, because it gives a faulty reading. I have been told by my mechanic that low fuel pressure could cause the symptoms I have. I do believe this to be true, but definitely looking for additional opinions here.

I've got another thread looking for a cheaper fuel pump - so if I can do that I will be happier. (Yes, checking eBay but trying to figure out if those REALLY cheap pumps fit.)

Let me know your thoughts here. =)

[GasSavers_bobski]

Originally Posted by 101mpg

The fuel sending unit (fuel pump and fuel gauge sender) needs to be replaced, because it gives a faulty reading.

They're separate parts. The fuel pump is attached to a carrier in the driver's side rear corner of the tank, and requires that the tank be dropped off the car for removal. The fuel level sender is at the front of the tank, near the middle. There's an access plate over the sender (it's under the cargo organizer bin thing) that the various fuel tank wiring passes through. You may be able to remove the sender through the access plate opening, rather than drop the whole tank.

If you really suspect a fuel pump issue, I would check that the pump is getting good voltage before replacing it. The Main Relay, which controls power to the ECU and fuel pump, is a common failure point in our cars. If your relay is approaching failure, it may be restricting power flow to the pump, resulting in lower than normal pressure. Like I said, all the wiring for the fuel tank, including the fuel pump wiring, runs through that access plate under the cargo bin. There's also an electrical connector there... Just back-probe the appropriate wires (blk and yel/blk most likely) with a multimeter and go for a drive. When the problem manifests itself, take a look at the meter.

[Mayhim]

I had the RPM hunting problem a couple of times. It didn't manifest itself completely as you described, though.

I fix mine by a couple of cycles of unhooking the battery and letting it relearn it's job.

Good luck, whatever it winds up being.

[Gary Palmer]

I have an 89 Honda wagon which had that problem. In my case it turned out that IACV valve had failed and was leaking excess air into the intake. When I pulled the air hose, to the IACV valve and plugged it with my thumb, the idle settled back down. I replaced the IACV valve and have not had the problem, since then.

I think what causes the hunting is that the ECM is either not getting an input it thinks it should, or is not able to control something it thinks it should. Best of luck. I don't think the hunting rpm is related in any way to the fuel pump, fwiw.

[101mpg]

Thanks - now I'll research IACV and check it out.

By the way I have an additional problem - have an aftermarket cruise control and it cannot hold speed. If it's not getting enough vacuum because of an IACV leaking excess air into the intake that might solve two problems. This seems very plausible and I am definitely going to check it out as soon as I have time!