idle evens out when i create a vacuum leak, revs on its own.

[penciltester]

Got her back on the road, she is bogging down on acceleration intermittently. Checked for any obvious vacuum leaks,thanks Dave, and found the hose connected to the back of the cpr was barely on. I secured it and went around the block again, still bogging down. It also starting to rev the engine when my foot was off the gas. I pulled it into the driveway, and let it idle. After a few minutes it started to bottom out and then rev, like a really bad idle hunt. I thought maybe my mixture was way off so I pulled the plug to adjust the mixture. Soon as I pulled the plug and heard the whistle of the vacuum leak the idle evened out.

frequency valve buzzing away.

Things changed/installed: fuel distributor(hooked the dwell meter up to adjust mixture), fuel pump, fuel accumulator and hoses, stage one exhaust, new slave cylinder, new leather, new thermo time switch.


any help is always appreciated.

Thanks!

[Ron]

Since it evens out when you pull the CO plug, I have to ask if you are plugging it when you take a reading...you should.

[Bitsyncmaster]

What was the RPM when you added a vacuum leak? If the idle RPM goes to high for whatever reason, the idle system can not compensate and it goes open loop idle. That would stop the hunt. A common problem causing idle hunt is a dirty idle motor. So adding a vacuum leak makes the idle motor run in a different part of it's rotation and may fix the hunt for a while.

[penciltester]

It was bouncing from 500 to just under 1500.

[David T]

It was bouncing from 500 to just under 1500.

To get the idle quality right you must get everything else right first. If necessary the motor should be tuned up, the valves adjusted, filters changed, no vacuum leaks, etc. Make sure the 3 brass screws are lightly seated closed. You may need to clean the idle motor so it works without sticking. The O2 sensor should be working and the motor at operating temperature.

[penciltester]

Thanks guys.

What's odd is it only seems to do the massive idle hunt AFTER I run it down the road, also bogs down. If its just idling in the drive way, hasent ran down the street,it doesn't seem to hunt.

When I run it down the road and I get to a stop, setting in first, it idle hunts. Reving the engine. I come back and park it, continues the big idle hunt.


Would a faulty thermo vacuum switch or solenoid be an issue?

Thanks again guys, I'm learning alot from this community.

[Bitsyncmaster]

I would concentrate on fixing the "bog down" issue and not worry about the hunting for now. Most common low power causes are mixture or timing. Have you checked both?

[Soundkillr]

Check to see if there is vacuum going to the WUR after the car is hot. If there is, that is likely your problem. There is a solenoid under the intake the turns vacuum off to the wur once the car is hot. If it has vacuum on it when hot, it will bog like crazy and stutter. Mine did this, ran great when cold, but once hot ran like crap. Pulled vacuum line off the wur and it ran great. Causes the car to load up on fuel and do weird stuff. Next day I installed the solenoid and never had anther issue....

[penciltester]

Thanks guys. Ok, so we already did a dwell test and my dad dialed it in, hole plugged. Timing, not yet. No vacuum to wur after warm up.

When listening more to the engine,reving it and the like while parked, when the engine stumbles and bogs the frequency valve shuts off/no longer buzzes. Ideas? or should the FV turn off/on while running?

thanks again

[Bitsyncmaster]

Thanks guys. Ok, so we already did a dwell test and my dad dialed it in, hole plugged. Timing, not yet. No vacuum to wur after warm up.

When listening more to the engine,reving it and the like while parked, when the engine stumbles and bogs the frequency valve shuts off/no longer buzzes. Ideas? or should the FV turn off/on while running?

thanks again

FV should always be buzzing. I have seen a few stock RPM relays faulty in that the second output did not turn on and that would kill the lambda system (not run the FV). Mine did that and another owners brand new one also had that problem.

If you make up a double jumper, jumping the brown wire to both the white/purple and brown to the double yellow/red wire on the RPM relay plug you can see if that fixes the problem. You can run the car like that but would need to remove the jumpers when you stop the engine or it will continue to drain the battery.

[penciltester]

I had another rpm relay laying about, the old one we replaced when we replaced all of the relays with a new relay kit. This relay was working fine at the time. No diference.

I had read something about some guys having troubles and they ran the system with the oxygen sensor unplugged. Tried that, no improvment.

We shut the lights off checking for sparks and arcs, no luck.

Checked and cleaned grounds in the engine bay, nothing.

Next step is pulling the injectors to see if there is a flow problem. Also is there a way to test the vacuum solenoid for malfunction? Any other ideas? REALLY dont want to have to ride into the VOD if it can be avoided.

Thanks again.

[Bitsyncmaster]

Also is there a way to test the vacuum solenoid for malfunction? Any other ideas? REALLY dont want to have to ride into the VOD if it can be avoided.

Thanks again.

I did find a bad vacuum solenoid on a friends car. Found that by using a timing light and it only advanced half of what it should be. Measured vacuum at the input side and it was correct. Measured it at the output side and it was half of the input. So I'm assuming the vent in solenoid was stuck open and it just happened to drop the vacuum in half.

[penciltester]

Thanks for the prompt reply we will take a look at it.

Another thing that just got interesting, I went to check the dwell again.....it bottoms out to 42 and will not change reading, stays put. So, could this all be electrical? Is this a sign of a bad ecu? How would I test it?


Thanks again!

[DMCMW Dave]

Thanks for the prompt reply we will take a look at it.

Another thing that just got interesting, I went to check the dwell again.....it bottoms out to 42 and will not change reading, stays put. So, could this all be electrical? Is this a sign of a bad ecu? How would I test it?


Thanks again!

Stuck at 42 means that the O2 sensor is either fouled or disconnected. If you click the switch it should go to 55, and there are some tests listed in the manual involving a 1.5 volt battery and a ground wire that will very effectively test the ECU.

[penciltester]

Heh, well right before we were about to pull the intake manifold I detached the grounds in the engine bay again. Cleaned again, but I moved the ground for the oxy sensor etc.. To a different spot on the manifold. Fixed the bog down and stumble.

*sigh* feel like a jackass, but hey at least now its my choice to dive into the VOD and not a necessity. :)

You guys have been awesome with all the help.

A HUGE thanks to everybody!