98 Villager - engine surging

I'm test driving a 98 villager, had a 94 for 212,000 and looking to get one with fewer miles. When I'm on a hill or accelerating it seems to be surging a bit. Not enough to show on rpm put you can feel it, on/off, on/off with a rhythm to it. It is suppose to have had new plugs and wires recently. I've checked over vacuum hoses and look good. Checked air filter, and mass airflow screen - clean. I've ran Lucas injector cleaner through also. There are no check engine lights coming on either.
Sprayed cleaner in throttle body and sea foam in intake but nothing so far seems to help it. I don't want to buy it if it is something major that I don't know about. Seems to idle fine and has plenty of pick up in acceleration, the surging is just annoying at this point but don't know if it would get worse or cost a lot to fix.
Any ideas of what to check would be appreciated.

How many miles?

Stop by a autoparts store and get codes read for heck of it, there may be some stored codes even though no CEL on.

Do you know of anyone that has a AutoTap scanner tool (google autotap.com to see what it does)

Try unplugging 02 sensors and see if that makes a difference.

Check fuel pressure.

If the surging isn't showing on the rpm's I would think it's in the tranny. I would check codes in the tranny control module(tcm).

the van has 128,000 on it. I put a new fuel filter on it last night though the old one was only on for about 10,000.
Seemed to help some, but when you step on it for freeway entrance ramp the up and down is still there. There is a slight rpm change, but not drastic. Auto parts fellow thinks it is possibly throttle position switch but at 98.00 hate to put it on just to see, espcially when it's not mine yet. Wonder, could you get one at the junk yard to see if it changes things? Plulled one plug - only 10,000 on them too - seemed a bit black like it's running rich. I'm going to try and get the codes read today if I can find a place to do it. Pulled vac hose off of fuel regulator and not gas coming out - so hopefully that is ok. Have no idea of what they get to check codes on trans. thanks,

Remove the distributor cap and look at the optical sensor for any dust on it. Villagers have a tendancy for the bearings in the distributor to go bad.
Just a thought.

Replaced the fuel filter the other night - seems to help a little bit on the surge
Had a mechanic drive it, thought it was the throttle position sensor, so got that and put it on. Still surges somewhat - would like to get if fixed so I know I don't have some other big issue waiting to go bad after I buy it. I'll try and check the optical sensor for dust tomorrow. Any other ideas - would be appreciated.

Did you try disconnecting 02 sensors to see if makes a difference? Checked for any codes? Do you know of anybody that has a scanner that you can hook up and take for drive to watch all the live data?
A laptop with software like autotap.

I haven't tried disconnecting the 02 sensors yet -
I did check for dust in the distributor - on the disk - didn't take the optical off as I had no special cleaner to use on it - didn't want to mess something up if it had to be in a set postion to read the disk. It had some kind of lock material on the screws. I did put in a new throttle position sensor. Still acting the same. When our run the engine up a bit you do get a slight variation in the rpms - like some kind of a miss or something. The plug wires seem to be fairly new, is there any way to check them with an ohm meter or something incase one of them are bad? There are no check engine lights and everyone I've talked to said if there is no light their scanners won't show anything. As it's not mine yet, hate to start replacing a lot of parts just to see if that is the problem. Thanks for any ideas.

"Measure the plug wire's resistance, end to end, with an ohmmeter. Refer to
the vehicle manufacturer' s specifications, but, as a rule, resistance should
not exceed 8,000 ohms per foot. Replace the wire if resistance exceeds
specifications."

I would check for codes at autozone, they do it for free. There may be codes from the past still in the ECM even though the lite is not on. Sure not going to hurt by checking.

The optical sensor (camshaft sensor)is a part of the distributor and the whole distibutor needs to be replaced if faulty.

Could also be a faluty injector. Try removing several spark plugs to see if they all look the same since you feel one looks like its blackish from running rich, this may show that you may have a sticky injector.

Have you tried driving with the O/D off or in 3rd to see if it still surging?

Still surging -
Took it to have it scanned, show rear O2 sensor and MAF - replaced both - didn't help. Took it to transmission shop - scanned and no codes or problems. Trans. mechanic said maybe Idle Air Control - those are expensive. Trying to read up on how to clean it - it's on top of the motor and hard to get at. Any more input?

Here is a link for a Factory Service manual for Villager/Quest:

http://www.nicoclub.com/FSM/

scroll down to quest, click on it and choose year.

Go to Section EC Page 184, it has some tests to do with the rear 02 sensor.

I am thinking you still have a problem with either the rear 02 harness or fuel pressure.

What was the code #???

Was regular code scanner used or did they check it out with a scanner that shows live 02 data??

Hope this helps.

Surging sounds like a intermittent lean condition. An exhaust leak may be playing with O2 sensors. Spray some WD40 or starting fluid up around the Intake and listen for rpm change. Could be an vacuum leak. Clean the MAF wih MAF cleaner, then disconnect the battery for 30 minutes to reset the computer. It sounds like a sensor is bad, which one is the question.

I've had a bad wire on my 2000 and the engine will stumble, not surge. Sounds like AF ratio problem. Pull all the spark plugs and check each for abnormalities.

Boy that throttle position sensor is sounding suspect now that everything else has been looked at. If you know someone with a villager, swap out the part and see if it helps.