dr bob

From the gauge reading the thermostat probably isn't the problem. Lower detected temp (from temp-II sensor) causes the engine to run richer, and that will help mask a vacuum leak. When it does actually get to temp and the LH leans out the mixture thinking the engine up to temp, then you are seeing the problem.

In the last few years there was a RL thread about pieces needed to test pressurize the intake to help find vacuum leaks. Common Home-Depot drain pipe fittings and a natural-gas test gauge that reads pressure in inches of water column. Connects to the MAF where the air cleaner joins it now. Need a small air compressor but not much hopefully. I think Roger sells the package parts as a kit. Anyway, if you have vacuum leaks, and your symptoms say you still might, it's a cheap and easy DIY way to ID them.

Mongo

It would have to be a big vacuum leak to cause that though, wouldn't it?

fraggle

Not sure what else you worked on, but check the 02 sensor. The mega-rich running may have ruined it.

Mongo

The O2 sensor was replaced prior to these fuel dampers. We are talking in a period of within 3 months ago. The thing is still shiny in the exhaust I'm sure.

I don't know why but I have this feeling it may be that low temp thermostat. Prior to doing the intake service, I was running really lean. I put a low temperature thermostat in to solve a running hot issue back in 2004 and it had ran fine for a long time. After the intake manifold service and moving to a colder environment I had noticed the car burning a little more gas than usual. It could have been because the dampers were failing and the LH was overfueling the engine because of the Temp II readings with colder coolant coming in from the radiator.

A thermostat can't be more than $30 so I'm curious to give that a try. Overall, I am VERY HAPPY with how she runs though and I really am not bothered by the shudder at idle. Then again, it may be embarassing stalling out at a stoplight when the temps are getting too high.

Mrmerlin

so right now your waiting for a new fuel line to test the new fuel dampers??
did you also replace the fuel regulator?? this is the one at the aft end of the passenger side fuel rail (Regulator)

dr bob

No. A big leak makes it tough for the cold-start enrichment to make up for the dilution. It would idle poorly from a cold start. The fact that the idle is OK until it warms up would have me loooking for a smaller leak. It could be as easy as a hose connection, or that broken Y in the breather system next to the throttle body/MAF boot. Or any of the oil breather hoses, or a cracked oil filler, or a loose oil filler cap, since air there is drawn in after the airflow sensor so unmetered air. It doesn't take much on the actual vacuum side of the throttle, but unmetered air from the breather system would do it too.

Mongo

No no, it's all assembled! I'm running Mako 928's old fuel line as a bandage right now and it looks a lot newer than the one on my '87. The regulator has already been replaced as well as the dampers.

Mongo

Dr Bob,

I checked all the hoses and verified the clamps are tight. The Y next to the intake is not leaking either, nor do I hear any hissing around the engine compartment. I agree with you on checking for vacuum leaks. Prior to replacing anything, introducing a vacuum leak into the system actually kept the car from stalling at operating temperatue. Something is telling the LH to overfuel the car when it's warmed up. On the road and in motion, nothing is irregular.

Cosmo Kramer

Have you checked for vacuum on the line going to the FPR? If that line has a vacuum leak it would cause higher fuel pressure at idle and rich condition. This is probably OK when it is cold as more fuel is needed but once warm it would cause idle problems. Putting a gauge on the rail will tell the story.

Mongo

When I was back there doing the dampers, I had verified that all vacuum lines are properly seated in the 5-way splitter and on each of the diaphragms. No leaks there!

Bill51sdr

Andy, see your email regarding your fuel lines or call me. You need to replace all of them ASAP! I have some old rebuildable ones I can get to your Dad.

Mako 928

On a side note:
The fuel line I gave Andy is the one in front of the engine and goes from the fuel rail to the dampner.
Mine had been replaced from a previous owner and I replaced it again from the fuel line hose kit from roger. This is the factory hose Roger supplies with his kit.
This was used only to get the car running and to trouble shoot.

Mongo

New one is still en route today.

Mongo

By the way, the fuel lines I KNOW NEED REPLACING are #8 and #10.

Bill, I know you are considering sending me your lines to rebuild, but wouldn't Roger's repair kit cover this line???

Mako 928

#6 is what we replaced yesterday and what is comming today.
#8 looked good but I would use factory to replace.
#7 is one of the lines Rogers kit provides and I have enough hose and clamps left over to replace on yours.
Not sure of #10 for MY '87. If Rogers kit is used for this I do not have enough left over to replace.