Surging Idle and while steady on the gas

1990 LINCOLN TOWN CAR

51,599 MILES • 5.0L • V8 • 2WD • AUTOMATIC

FLAZ

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4 POSTS
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Okay, so I got the car listed above in near mint condition, it is the Signature Edition from my neighbor. I purchased my home in 2014 and she finally sold it to me this year (2022). It has 51,000 miles on it. Not bad for a 32-year-old car. So, I got it changed all the fluids. Got a new fuel tank, fuel pump and filter (all installed). New battery and single wire alternator. I also replaced the battery cables. New plugs, plug wires, distributor, cap and rotor as well as coil (all MSD). Air filter, new tires and hoses. It fired up and ran quiet and smooth. But that was before I changed the plugs, wires etc. It started lurching or like surging. So, I thought maybe that would help. It didn't so I looked for opinions or ways to fix it, so I replaced the EGR. And nothing still does it. Any recommendations? I'm trying to get to running so we have another good car. Thanks again!

I almost forgot I changed the oxygen sensors as well. And the u joints and Transmission oil seal.

Mar 30, 2022 at 11:27 PM

KASEKENNY

CERTIFIED EXPERT
18,907 POSTS

Surging could be a couple of things so let's start running through these couple of guides that will cover the basic items that will cause this:

https://www.2carpros.com/articles/engine-surges

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

However, if all this started before changing the plugs, can you get a picture of them and see what they look like?

They may be able to tell us what is going on.

So, let's start with running through these items and then get a picture of the plugs and we can go from there.

Thanks

Image (Click to enlarge)

Mar 31, 2022 at 7:14 PM

FLAZ

MEMBER
4 POSTS

Hey Kenny! Thanks for the response. I checked but I already tossed the old ones. They didn't look bad, they just looked like 32-year-old plugs. They were the original Champion plugs from when it was purchased. Well, I don't know that for sure, but they were old. But they didn't look burnt, broken or soaked.

Mar 31, 2022 at 7:57 PM

KASEKENNY

CERTIFIED EXPERT
18,907 POSTS

Okay. So, we need to do a couple of other things. First let's try and clean the mass air flow sensor as these older Fords were well known for having surging issues due to incorrect air info given to the PCM. This is assuming that you have CA emissions which most vehicles do. If you have Federal Emissions, then you most likely don't have a MAF sensor.

https://www.2carpros.com/articles/mass-air-flow-service

If this checks out ok let's run through this guide and cover all these items.

https://www.2carpros.com/articles/engine-surges

Keep us posted.

Apr 2, 2022 at 7:59 AM

FLAZ

MEMBER
4 POSTS

Yes, it doesn't have a MAF sensor.

Apr 8, 2022 at 8:54 PM

KASEKENNY

CERTIFIED EXPERT
18,907 POSTS

Okay. Next thing then is we need to find out what the o2 sensor data is showing.

Basically, I suspect it is going to show that it is lean and trying to compensate for this.

This means the o2 sensor is telling the PCM that it is too much air in the exhaust and so it adds fuel. Then it starts to richen, and it backs it off. However, due to it having this lean condition you get the surging when the fuel is adding and then pulled away.

Then we need to put a vacuum gauge on this intake manifold and see if we have an intake valve issue.

By doing this we will find out if the intake valves are hanging open which will cause too much air to come into the engine and lean it out.

I attached charts below that will help with figuring this out.

Images (Click to enlarge)

Apr 9, 2022 at 7:09 AM