Car: 1998 SE

Recent maintainence: bosch platinum plugs
new plug wires
new air filter
new pcv valve
new o2 sensor

Problem: Some days the car lightly surges when driving at a constant speed. Usually changing speed or accelerating causes it to go away. Dosen't happen every day, just occasionally. The problem was present before and after the plugs/wires were replaced. I should replace the fuel filter, planning on doing soon. I also have a tranny service planned using the lucas additive. Problem seems to be hard to duplicate. Searches on this forum bring up a multitude of potential issues for similar symptoms, from EGR valve to transmission. I am not throwing a MIL light in the car. Can anyone help with some ideas? Thanks

Bosch Platinums are perhaps the worst plugs you can put in your engine. The electrodes will extrude/erode variably by the time you've had them 30 days. If they last 3 months you'll be lucky. They don't like living in 3800'* for some reason. MANY members have had problems with them.

I suggest replacing them with AC Delco or NGK plugs (NGK makes the Delco'*).

Your problem doesn't sound like an ignition or fuel stumble to me. It sounds more like the typical TCC surge in 4T65E'*. Do a search on "shudder" or TCC shudder. You'll find lots of info here on it.

I might have to agree on this one..... This problem is also present in 4T60Es, like in my application. Not sure if the 1997 tranny fix bulletin is applicable to 98s, but it could be a worn valve body. Do like willwren said and search for 'shudder' or 'surging.'

Remove the IAC, MAF and clean it as well as the throttle body. Use intake safe cleaner.
Have you run fuel injector cleaner and changed the fuel filter? Probably wouldn't hurt to check fuel pressure at the rail schrader valve.
98 also had an issue with the fuel regulator. Remove the small vacume hose to it and check for gas smell. If you smell gas you need to replace it.
Check with your dealer as it may be covered on recall.

Allright,

Fuel filter still needs to be changed. It'* sitting on the workbench waiting. I will follow advice and replace the bosch platnum plugs with another brand. I should have known .

On another note, the car tripped the MIL so I took it and had the codes read. 2 codes were EGR related and 1 was the VSS. Did a little reading and it seems that both EGR and VSS problems can cause surging. It seems the VSS controls xmission line pressure, shift points, and possibly lockup solenoid engagement. This would also explain why it seems that my shift rpm under light acceleration is high. This is my first Bonneville so I didn't know what was characteristic or a potential problem.

Next steps -
1. Replace plugs with suggested type
2. Clean mass air meter, EGR, TB. Anyone with links for pics and/or instructions?
3. Replace VSS. Does anyone have part numbers for my application? I have done quite a bit of shopping on ebay for new/unboxed items such as this at quite a cost savings. I would like to have OEM and/or replacement part numbers on hand so I don't order the wrong part.

Thanks for all the information and suggestions. I will update this thread with the results of my work for others' future reference.

Here'* a quick link that describes the MAF and TB cleaning. I just ran out of time for searching, but I know there are a couple good pics of the TB on here if you need them.

TB & MAF Cleaning

BOSCH PLUGS - I am one of those members with the problem, but it was not in the 3800.
They are not a good idea for most engines. Maybe in Germans cars, but not U.*. cars.
I once ran them in a 2.2 chrysler engine, a reliant K, (no where near related to our 3. and once the first truely cold spell hit, the engine would NOT start til after replacing the plugs. (A fun job in negative ° weather in the snow)

Does anyone else think that higher RPM than normal shifting (during normal driving) and the intermittent "shudder" could be caused by a failing VCC? Anyone with OEM factory part numbers for replacement VCC'* or able to tell me where to get them?