Really bad idle on CIS

MysticLlama · 04-19-2006, 03:54 PM

I tried to get in today to just get a mixture check, but wasn't able to, and after observing it more I'm not sure if that's all there is to it.

First, chain of events:

Broke a motor mount.
Replaced both motor mounts with WEVO ones.
Dropped the engine a touch too far and lost the connector for the cold start valve, was very hard to start.
Figured that out, reattached, starts fine now.

Haven't driven the car much until it's been warmer out, so I thought mixture, but it's been really far off before and never this bad.

The car runs fine once it's going down the road. It doesn't seem to have any more/less power than I remember it having, revs freely.

The problem is idle, or engine speeds below about 2500rpm.

It's fine when cold, the issue starts once it's warmed up.

It will sit there and idle at ~1000rpm, but does lots of quick bumps of between 100-300rpm, runs really rough. Not really a sweeping hunt of a range back and forth like I had with mixture problems.

When it bumps up, sometimes it makes a rattling noise. Not sure if it's the engine or some accessory rattling, but it doesn't sound healthly either way, and it's not a noise I had before at the rpms it's hitting. (pinging?)

I've checked all of the connections I can find and they all seem tight, removing the oil cap lowers the idle a bit, but it acts the same, plugging in or unplugging the O2 sensor makes little difference.

Where do I go next?

I'll try a few more things and if it can't be identified I guess I'll take it up to a shop when I can find someone that has time. If this does sound like pinging, I'll probably just have AAA come pick it up.

MysticLlama · 04-19-2006, 03:56 PM

One more thing, it did blow the popoff valve at one point yesterday in traffic and the engine shut down.

I didn't really hear it, but when it died I could see a little smoke out of the rear grill, which is what happened last time the popoff went off. It started back up and kept driving though, and made it to work and back today.

1fastredsc · 04-19-2006, 05:09 PM

Watch the fuel metering arm/plate while it idles. When the fuel distributor starts giving you some problems, it sometimes oscilates which would cause it go lean and rich in that oscillating manor. My fuel distributor was starting to do that before i took the engine out, however it was oscillating so minutely and fast at idle that it didn't make much of a difference. And if i would rev the engine it would smooth out.

MysticLlama · 04-19-2006, 05:17 PM

Is that the same thing that's under the air cleaner that makes the injectors whirr when you press up on it?

Or is it something up by the fuel distributor itself?

vash · vash's Garage

i bet you forgot and inadvertently disconnect a vacumn hose.

1fastredsc · 04-20-2006, 06:05 AM

Yeah it's behind the air cleaner, might also want to check what vash said as well.

jjone20 · jjone20's Garage

How old's the gas? What quality? I had some of the same symptons and just before I tore into the CIS I filled up with good gas and it was fine thereafter.

wesayso · 10:02 AM

If the problem gets worse when warm I would check ignition/wires. Drive it on a dark night and open the lid to check if your cables are fine.
It sounds like you where getting this problem from dropping the engine but it could be coincidence.
I had a hard time tracking down a rough idle and hesitation till about 2500 RPM and it was the wires shorting when warm.

Here's my story:
Hessitation solved on a '82 SC (long write-up)

MysticLlama · 04-20-2006, 10:13 AM

I think I checked all of the vacuum hoses I can get to, multiple times, they all seem hooked up.

Gas is 3 days old, Premium, has done this for a couple of tanks now, it's just a lot more regular recently.

I'll get it warmed up in the dark and check it out. Should I expect to see something, or do I need to add a little to it? I thought back working with my dad on a car that we misted water over them or something to make them arc, but I'm not sure if that's applicable/recommended.

The plugs/cap/rotor/vacuum retard unit are all only a little over a year/20k miles old maybe.

It does seem to be related to the engine drop, but yeah, not sure. It was only dropped about 6-7 inches, just enough to get the crossbar out while wiggling it around.

Had Scooter over last night and we both think it sounds kinda like the fan is scraping the housing, but why would it only do that at such a particular rpm range?

wesayso · 04-20-2006, 10:27 AM

The water would enhance the effect but I could clearly see blue arcs on the wires near the cap. You didn't mention having the cables replaced so that could be part of your problem. Once I began to suspect my cables I could even hear them short. That's when I decided to go out at night to check it out

Good luck and let us know!

Mysterytrain · 04-20-2006, 10:34 AM

My 78 doesn't see much winter weather driving but this season was so mild and snow/salt free that I was able to drive it. I noticed that on very cold start ups the idle would hunt, climbing to about 2k and drop back down to 400 rpm or so for a couple of minutes before it sorted itself out. I know that I have my WUR set a little rich and I need to readjust it. I'm thinking you might have the same problem. Have you checked your pressures lately?

wesayso · 04-23-2006, 12:28 PM

Any luck with the test? Hang in there, you'll find your problem.