'87 R20 rough idle/detonation.

[TFBC]

I have an '87 R20, TBI 350/TH400. When it is started(with the engine cold), it shakes fairly bad, idles rough, and detonates some(it does not smoke while doing this). Once the engine starts to warm up(at about 125-130 degrees), it idles smooth, and runs and drives fine.
The truck is all stock, and the engine has 18,616 miles on it.
It did this three times last winter, but for the last three weeks it has done it everytime I start it(in both warm and cold weather). About a week ago the check engine light came on, with a diagnostic code of 45.
When it first started doing this(three weeks ago), I took the EGR valve off and cleaned it(there was very little carbon build-up), but it did not make any difference. The EGR valve moves freely, with no sticking or binding.
Any ideas?

[rwhit57]

It kind of sounds like a vacuum leak or the intake itself is leaking.

[Desert1957]

When engines run rough at any time always remove all 8 plugs for visual inspection. You will be surprised how much info a spark plug can tell you.

Here is a good read....

http://www.gnttype.org/techarea/engine/plugs.html

Desert