1990 Fleetwood - Rough Idle

[gofast123]

Thinking about buying a '90 with 53,000 miles on it.  I'll see it in person on Thanksgiving morning but the seller already told me that it's idling rough.  Other than that, the seller says it's an extremely clean car.

Just looking for some "best case / worse case" scenario possibilities from the forum. 

Anything I should look out for in particular?

Thanks in advance...  Gary Hodges

[waterzap]

Best case. Vacuum leak or something simple like a bad fuel injector, bad plug, wire, ignition coil. Timing could be off.
If it only idles rough, but runs fine, I would tend to think its a "simple and small" problem rather than the "big and expensive" one.
I think this is the 4.5 or 4.9 engine?

Check the oil. Should look like oil and not milkshake.
Coolant, check the transmission fluid. Tell the guy to leave the car and not start it before you get there. See if it starts easily.
Look at where the car is standing. Puddles of oil, or little drips?
That’s about all I can think of. The 4.5 and 4.9 were good engines, but you can still have coolant leaking into the oil, which is something you want to look out for.

[936CD69]

Assuming you are talking about a FWD with a 4.5, they are known to drop injectors. If the injector resistance goes way out of range the PCM may also need replaced. Not a huge deal if the car is nice otherwise, but figure $3-500. If one injector is bad, replace them all at once

[gofast123]

It is the 4.5...  do all the 4.5 and 4.9 have the coolant leaking into the oil issue?  is it inevitable in all of them? 

why does this happen and can it be prevented? 

I ask partly because I just bought a '93 DeVille with the 4.9 with 40,000 miles on it...

[waterzap]

I have a 87 4.1 which is still running fine. Don't think the 4.5 had as many problems with the coolant leaks, but I guess it is still possible. Use the GM tabs, change the coolant and oil regularly, and you should be fine.
We are after all only talking about an intake manifold gasket that goes bad.  If the manifold gasket starts leaking, look for the symptoms, and  just have it replaced. Not the worst thing in the world.

Also check the oil often, glance at the water pump now and again to look for weeping.
I do think the water pump is not a great design. Being long and shallow, but I guess that's all they could fit.

[Dave Shepherd]

All good advice, but from a diagnostic standpoint he really has no idea what the roughness is, as mentioned could be an injector, or wire, or plug if it is a misfire, or again. as mentioned a vacuum leak,  Some checking is called for here to try and pinpoint the misfire cylinder, if in fact that is the issue.

[Guidematic]

 The 4.5 was a great engine, especially by 1990. that was the first year for PFI on these engines and they were good for 190 HP.

 Yes, injectors were a common culprit, but I would have a look see at the car first and come to your own conclusions.

 FWIW, I have heard the injectors from a Chevrolet TPI engine work very well in these engines, and are considerably cheaper. It must be noted that Bosch manufactures the vast majority of these injectors and there is a great deal of interchangibility. However you need to look at the resisitance and the flow rate of the injectoras to make your choice.

 Mike

[76eldo]

The 4.5 and 4.9 engines were not know to have the same issues as the early 4100.

Coolant changes and adding the GM or Barr's leak pellets is recommended.

Brian