Car has running issues

[oldscutlasswagon]

Hello all. I have been doing quite a bit of work on my wagon lately and recently it started running very poorly. Here are the symptoms. On WOT the car seems to run like normal, but cruising it starts surging and momentarily losing power. It has hesitation off the line and starts hesitating even with steady throttle. I hear popping sounds while driving and a rattling sound as well...
The car is all factory including all the smog equipment (I live in CA), new air pump, professionally rebuilt factory carb and new gasket, new fuel pump/filter. No CEL's and all the ignition stuff is in good condition.
I have gone over the vacuum hoses twice over and have replaced all bad hose. The carb is also correctly fastened. I am sure it is not a fuel issue because during a trip over a mountain (literally) it runs normal under long WOT stints, which also makes me think it is not ignition related but I checked the plugs and everything looked fine.
When I first got the car I did pull the EGR and clean it up and reinstall it. However the rattling is making me think this is the culprit. Does this sound like I am on the right track?
I manually moved the EFE valve and it doesn't appear stuck.

 

[Jeff L]

I remember a friends car ran horrible when the EGR valve malfunctioned. Stalling and poor driveability. This can happen when it leaks, bad gasket, or a loose valve like you mentioned. Improper vacuum can mess up the idle and cause stalls, surges, etc.

Hope this helps.

Jeff

 

[ed1948]

Attach a rubber hose to the EGR fitting...suck on the end of the hose and feel for the EGR diaphram moving and staying retracted when you squeeze the hose to hold vaccum or place your tongue over the end.
From my experience the car will barely idle with a stuck open EGR but run fine at driving speed.

rattling - could it be pinging?

 

[Texas82GP]

Sounds like a lean condition. Could be because of EGR or something else. Did it ever run good with the rebuilt carb? If you wanted, you could rent a hand held vacuum pump from the auto parts store to test the integrity of the EGR diaphragm. See if it will hold vacuum.

 

[oldscutlasswagon]

While vacuum is applied should it hold vacuum or allow some leak-by? I am assuming when the EGR is removed I can see the mechanism and will be able to tell if its moving. The rattling isn't constant and doesn't sound like pinging. and happens mostly with the engine warming up still. The popping I mentioned started right when the car started driving funny, and happens when I go from light/no throttle to med/high throttle. Not all the time though.
I can't tell what the popping is but it isn't pinging. Kind of like a backfire sound but not as loud as an actual backfire. The car drives fine at WOT but terrible at cruise. Just to cross my t's... I removed it and reinstalled the idle speed sensor after the carb was rebuilt, but even if it was in a slightly different position it shouldn't affect off-idle driveability correct?. I can test it in the next few days but am tempted to order an EGR. Anyone have a ACDelco part number for a California EGR for 231v6? I only see them from other brands.

 

[oldscutlasswagon]

Oh looks like I got an answer about it holding vacuum, thanks. I will test that out. It did run well with the rebuilt carburetor and this problem started after it was already running. I will let you know what I find in next few days.

 

[Texas82GP]

I wonder if your timing chain may have jumped a tooth or two. That 3.8 has nylon tipped gears that wear away or break. Sooner or later you should put in a new chain and metal gears. How many miles?

 

[Bar50]

Does you vehicle have a vacuum advance distributor? It could be failing (leaking vacuum & not advancing), hence the part throttle drive-ability issue, at WOT its on mechanical/centrifugal advance.

 

[oldscutlasswagon]

The car only has 85xxx. I will check timing as well as test egr. Car does not have a vacation advance dist.

 

[pontiacgp]

If you install an air/fuel mixture gauge that will cut down on the guessing...