New a4 and first time Audi owner with a burning question.
 

I just picked up an Audi (1998 A4 2.8 quarto) thing runs perfect with one exception. The RPM's go up and down and it act as if its shifting up and down. It only does this when I'm staying at a consistent speed not when I'm accelerating or coasting. Also does not do it when I'm idle or in park. I've also found that if I use the "slap stick" (4,5, &6) it does not do it. So I really have two questions. Any one have an idea what my car is doing and also would it be bad to just drive around in 4th all the time since it runs fine when I do?

Sorry if I'm to new to be asking questions and jumped the shark I just don't want to be doing damage to the car I just got if I can help it.

Thanks for all your help!

Do the RPM's go up or is it just the needle?

Car feels like it shifts up then slips right back down and it will repeat over and over as long as you keep the throttle consistent. The RPM's and needle go from about 1500 to 2000 back and forth till you either let up or push down on the throttle or simply use the Manuel and put it in 3rd, 4th, or 5th.

I'm not nearly as knowledgeable as some people on this site but let's run through some scenarios..

it's only when you're at a constant speed? What about if you're idle in the parking lot?
Does it happen if you're idle? Does it happen at EVERY constant speed (10, 40, 60, etc?)

Disconnect the MAF and see if that helps. I had a same year A4 and the ECU acquires most of it's air/fuel information from the cats. You can also try a simple fluid and filter change. It's best to start with the cheapest solutions first and then go from there.

When you say fluid and filter change which fluid and filters do you mean? I just bought the car and I have a feeling it had been siting since last summer. What might you replace and top of and in what order? Thanks for any help!

If it's been sitting for awhile, do a throttle body adjustment. Either manually or with a VAG. The throttle body forgets how to react if it's been sitting for awhile or the battery was disconnected among other things. It MAY clear up your problem. Here's how to do it manually I think off the top of my head:

Put the key into the ignition and put it into ON position just before the starter turns (do not start the car), push the gas peddle all the way to the floor and wait 3 seconds and then turn the key all the way back to OFF but do not take it out, now release the gas and wait 2 minutes, remove the key and then put it back in and start the car.

The manual way sometimes doesn't work however, so it is better to do it with a VAG COM. And the instructions are HERE:
Ross-Tech: VAG-COM: Audi B5 VAG-COM Info

With the VAG, the main point to remember is, your codes need to be cleared or it won't work.

I'd try the adaptation first and then go from there.

If you have a VAG, let us know what the codes are. Or have them read somewhere. The VAG reader reads more codes and modules than a generic scanner from Autozone. The generic scanner will not read the throttle body module....but it will read the ECM and the TCM codes, but nothing else generally.

That might help. When I say to do a fluid and filter change, I mean on the transmission. Blauparts should have a kit available for the change.

Ya just had to do a tb calibration on mine tried the manually way multiple times ended up paying someone to come over with a vag to rest it 30sec later car was running great

Unless I'm mistaken, somebody proved that the so called "manual" throttle body alignment does very little if anything. In order to do it correctly you need to have VCDS, I would just buy it. It's $99 if you use a Chinese cable and it will come it helpful quite a bit