Cierra start-up problems

Any advice on this problem would be greatly appreciated;

The car:
1987 Oldsmobile Cierra, 2.5L, TBI

The Problem:
On start up (cold or warm) the engine acts like the timing is off. I
sometimes hear a "popping" sound like a backfire or firing into the
exhaust manifold. The engine may kill once or twice. After about 10
seconds it seems to settle down to a normal idle though a quick
depression and release of the throttle (while in park) will result in
the "popping" sound. Aside form this the engine acts normally;
acceleration, idling at lights and maintaining highway speed all seem
normal. Also my mileage has not decreased. This problem began four days
ago and was not apparent before that.

What I've done so far:
A vacuum gauge shows a strong and steady vacuum, I checked the trouble
codes but only get the normal "12" code, I disconnected (and
plugged) the line leading to the EGR valve but the symptoms remained
the same.

What are the most likely suspects to check next?

Carl

This could be a number of things: valve train components, retricted
exhust or yes timing may be off. Check the timing. DO A COMPRESSION
TEST ON ALL CYLINDERS. This will tell you the mechanical condition of
the upper end (pistons, rings, valves and seats or blown head gasket.
What does you reading on your vacuum gauge read a good normal engine
reads 17-22 Hg.

Hi Gary, Thanks for your reply. The vacuum reading was a steady 21 Hg I
just completed a compression test which showed 120, 110, 115, 120 on
cylinders 1-4 respectively. This engine has 130,000 miles on it. This
is a ditributorless ignition system so I believe checking the timing
would not be possible and is unadjustable.

The symptoms seem to be getting worse; on start up the engine seems to
not be running on all cylinders. After 20 seconds of so the rest of the
cylinders seem to kick in and then the engine idles normally. Rapidly
depressing the gas peddle produces a hesitation. While driving the
engine maintains speed fine but qucik acceloration again produces
hesitation. occasioanlly at idle at stop in traffic it seems to loose a
cylinder but slow and steady increase in throttle seems to restore the
cylinder and get me moving again.

I have replaced the plugs and wires as they were due for replacement
anyway.

For anyone who might follow this thread in the future the problem
turned out to be a faulty coil pack. The symptoms became worse as the
week progressed and finally it was "dropping" cylinders while at
idle in the driveway. As this was happening I began pulling the spark
plug leads one at a time to see which cylinders were not firing. The
two missing cylinders were serviced by the same coil so I was pretty
sure I had found my problem. On these engines there are two coil packs
both located on the back side of the engine facing the firewall.
Replacing them is easier if you disconnect the front upper engine mount
and tilt the engine forward a few inches. I used a ratcheting strap to
do this (the kind normally used to hold down cargo). Make sure to note
the spark plug connection order before you disconnect anything. I
replaced both packs as they are the same age (original from the factory
18 years ago. Not bad.).