Ok,well I am new to this forum been reading for days and days to try and figure out what the heck is goin on with my 2000 ssei and decided it was time to register and ask somebody for help.I will try to explain what is my prob as good as I can!I bought this car about 4 months ago and it has 111,000 miles on it so I decided to give it a tune up because she was running rough on idle,so....I changed the plugs,wires,,gas filter,trans flush,pcv,it had a k&n drop in filter already on it and thats about it.She still was running rough in idle.Then after having it for about a week or two I noticed that when i was cruising at 55 or so that when I go up a hill the car will start to jerk like its loosing power until I give it more gas and she downshifts.Also after I go to the store and she is warmed up and I shut her down to go in for a bit to do my shopping I come out to start her up to go home and she start to idle so ruff almost like she wants to die!I took her to the gm dealer they had it for a day and told me nothing is wrong that they can find out,arggggg!!!!!They did say they found in the history in the computer that there was a o2 sensor malfunction at one point in time but it seemed to be o.k.So I drove away thinking that maybe it was just me and after driving for about a half hour approached a hill and there it went again chugging up the hill to the point that when I look at the rpm gauge i can see it moving back and forth about 500 rpms.So I thought well maybe it is the o2 sensor so I went to the parts store got a ac o2 sensor to replace the one by the intake or should I say the first one not the one by the cat because I already knew that that one only tells you when your cat is going bad.I was so excited she seemed to steady out on the rough idle and I was happy!I went to work and she drove pretty good, got off of work and drove home and approached the hills I live by and sure enough there was that chugging again....damnit!!!!It also seemed to chug just going 25 to 30 mph in town as I approached home front!I wonder if it has something to do with the overdrive,iac sensor tps sensor hell I could guess and guess and guess!So the next day I thought well maybe it is the maf sensor,I have a 99 gtp and it runs like new so I took off the maf sensor from that one and put it on the ssei and drove around to see and sure enough there was the chugging up the hill and chugging going intown at 25 to 35 but only when it is in over drive it seems like when it is in over drive in lower rpms it does this hot or cold but more when it has watrmed up.GM told me that the compression is great and the intake and head gasket seem just fine!What the heck is going on here??????The rough idle has greatly improved though after changing out the o2 sensor but that damn chugging up the hill is really getting to me.There is no ses light coming on at all and it did chug when I went up a hill or after she sat for a little bit when I go into the store and come out before I brung it in to the dealer,since then the chugging has gotten more frequent and worse, I know that some codes dont always set off the ses light but the gm dealer said the only thing they saw in the history was the o2 sensor malfunction at one point in time.Please some one help me out I am really getting a big bump on my fore head banging my head on the computer desk trin to figure out what the heck is going on.I hope I gave enopugh info on my problem!Also I have runed a few bottles of chevron fuel injector cleaner through it to but to no avail it still chugs in od.I havent noticed the chugging after it has runned for a bit and i restart but I only did this earlier today and havent had the time to see.

now i don't know a whole lot about these sort of problems but:

it sounds like a fuel problem...possibly..

no SES light huh, and GM said no codes...

maybe your fuel filter is clogged...sort of unlikely

sounds sort of like what my car was doing when the engine was running so rich that it was choking it.

hopefully someone can help you...good luck with your problem.

Could you please tell me what or why your car was running so rich??

I'm thinking you may have a problem with your transmission maybe in the valve body area. Go to the Dealership and ask service manager if he would take your bonnie on a test drive with Tech II scan tool connected, go up hill to replicate the symptoms. He can force TCC engage and lock it in with the Tech II, this will eliminate the TCC mechanical & electrical as being the fault which leaves the valve body as the possible fault. The pulsations on the tach that you observed is the TCC engaging/disengaging.

I had a similar torque converter problem on a 97 Grand Prix. It would purr like a kitten until the RPM'* dropped in high gear going up a hill...then it felt like I was driving over logs and my RPM gauge was all over the place. All I had to do was mash the gas, it would drop a gear, and be back to normal. Unfortunately, I can't tell you how much to have it fixed as the thing had 148K on it so I traded it in towards my SSEi. Sounds like the same problem to me though.

Begin with the smalls easy things,

I would begin by cleaning your MAF sensor and throttle body. Mine was running hella rich and was struggling under llight to heavy load. I cleaned my MAF sensor and everything seemed to work fine.

The scan showed a normal voltage for my MAF, so this issue took a long time to solve, i changed O2 sensor without success, i changed crankshaft sensor without success, and finaly solve it with a 5$ can of AC Delco brake cleaner

Sounds like the car may be misfiring under load. Possible clogged cat? A clogged cat may have burnt up the old 02 sensor farily quickly as well as have been the original problem with the first 02 sensor.

BTW I would put your orginal MAF sensor back in as the 99 and 00 MAF sensors may be different.

Well thanx for the quick responses guys, well I forgot to mention that I did clean the throttle body and I did replace the maf sensor back to the original and I did make sure to clean up the maf sensor before putting it back in.When I had the car into the dealership they did check the cat and like I said they could not find anything wrong with it.I will try to take it back to the dealership again....argg another $80 spent but oh well I guess,and I will ride with them and have them monitor it for me.I just hope that it isnt the trans but I really doubt it but what do I know I am just a sous chef not a certified machanic.I just wish it was something I could figure out but then it would be a guessing game.I am pretty sure I covered all the basics on a full tune up so it can not be that.I will sure let everyone know what I find out out from the costly dealership.argggg!Just seems pointless to go back to the dealership,like I said they already had it for a whole day and a half and told me it was just fine but what the heck I will give it a try I am not ready to give up the car just yet.

bears, They shouldn't charge you another $80 for a second diagnostic. That is crazy. Speak to the service manager directly, maybe work out some sort of deal at reduced cost or preferrably no cost.

right, if they tried before and couldnt find anything, they should look into it further free of charge