Hey, This is my first winter with my 91' 245 and I'm hearing a "surge" of RPMs right at startup. On occasion the engine will "pulse" as well both after starting and idle. The surge is my guess around 2000rpm and usually drops down to a normal idle, although this morning it stayed steady at a very high idle until i turned off and turned the engine over a couple of times until it idled at a normal rate (no hard starts though). The check engine light has been on for about a year and a half (previous owner said it had been on for about a year, couldn't figure it out and had no troubles) and my diagnostic box doesn't work (no blinking) even though I did the procedure correctly.

From other posts similar to mine I hear to check things like
o2 sensor, AMM, dirty throttle body, and, vacuum hoses.

Anyone think of anything else?
I am a neewbie at this so please be patient.