Things to check:
Motor Mounts
Throttle Cable
Worn accelerator pedal linkages
Carbon buildup on valves
Spark Plugs
Trans mounts
Some Places remain unknown because no one has ventured forth. Others remain so because no one has ever come back......
I had purchased 98 540 a few years ago for $800, because the owner at the time was told car need engine rebuilt, it was smoking at start up, had little power.
When I got the car home, I replaced the valve behind the intake manifold. This correct the problem.
I would suggest to check the gaskets both front and back, you don't have to remove the intake the remove these parts.
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CSB is the Center Support Bearing on the Driveshaft - last on the list of Driveline mounts - and the most painful to change. Motor and Trans mounts are not bad. Guibo is a bit of a pain, but if he is cracked, or split, you will need to do it.
Thats a crankcase vent part. The diaphragm loves to go kaplooey. You need Dooneese hands to replace it.
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I have finally gotten back to this-did some research on fuel trims and 02 sensor v/trim...confusing. MAF shows 5.15 to 5.45. Seems good, was replaced by prior owner a few yrs ago. I replaced my air intake temp unit also as it was bad. I have a K&N filter, non oiled type. Car is throwing p0170/p0173. I did just order a purge valve as that is throwing a P0443 also but I don't think that would affect running.
02 S1 Bank 1 volts varies from .1 to .7
02 S2 Bank 1 volts varies from .1 to .3
02 S1 Bank 1 trim varies from -1.5 to +2
02 S2 Bank 1 trim shows nothing
02 S1 bank 2 volts varies from .7 to .1v
02 S2 bank 2 volts is real stable around .1v
02 S1 Trim Bank 2 varies from -2.4 to 0
02 S2 trim Bank 2 shows nothing
Update-I replaced the throttle body gaskets after a simple cigar smoke test revealed a leak at the top. Fuel mix codes are gone...
Still doesn't have instant response like I think it should. Saw a post about the 2nd butterfly, didn't realize there was one. On a v8 is there a 2nd one, and it's a bear to get the inner throttle body off, can't remember now when the outer one comes off, is the butterfly in that, or in the inner portion?
Is there a 2nd butterfly?
The second butterfly or throttle plate is in front of the main throttle. It is normally open and is only closed by the asc or traction control system.
Not likely to be involved in any way to your problem.
Vacuum leaks, followed by a dirty throttle position sensor would be my guess.
Then fuel pump pressure, vacuum leak to the fuel regulator, (also a pressure related thing), then you are getting down to small stuff.
Is it just your perception? Test drive another 97-8.
I did clean the TPS, did wonder about the fuel pump pressure, or vac leak. I need to check that...I've literally never seen another 540-8...I live in MI. Mine was stored, maybe they all rusted out, but they're not seen around these parts. Thanks for the tip. The fact that the car idles low and has an audible stumble at idle, and as it gets colder, it'll be some worse, are all symptoms that I can't figure out. Will try the fuel issue. I did suspect a pressure sensor issue also...
Vacuum leak would get worse when cold.
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Checked on the tubing at the fuel pressure reg, seemed good. Couldn't do my custom cigar smoke test (lol), no cigars! May remove the PVC if I get time and see how that all looks.
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