1997 Mercury 200 EFI rough start and idle

[Nitro29]

Serial Number: 0g469682
1997 Mercury 200 EFI

It seems I have sorted out a lot of issues with this motor, but one more has came about. All fuel lines have been changed and updated, new fuel filter, new plugs, compression checks 116-120 on each cylinder. All fuel is fresh. It is a devil to start initially at the lake. I leave the key on for about 15 sec, the bulb is hard, and it tends to take a few tries to get an initial fire. Once started, it dies probably 10 times before I can keep it running. If I try to give it any gas, it just shuts down, like it isn't getting any gas. Once warm, it seems to do fine the rest of the day. Throughout the day it has a rough idle, but takes off fine and tops out at 63 mph with a 24p Tempest Plus on a loaded 1997 Nitro Savage 896. Where do I start or what other information is needed?

[JOE54]

need to have sensors [ air & cyl head] tested along with fuel pres and link and sync done JOE

[Nitro29]

Thank you. I will start there.

[Tx 201]

Just went through that same scenario, and another guy with an older 200 EFI had the same problem. That ECU is 20 years old so I would guess fuel pump driver is going out. Don will be along shortly with some good advice for you, but betting he suggests the ECU is the problem. Got mine rebuilt and has been fine since. That and a good fresh battery.

[EuropeanAM]

need to have sensors [ air & cyl head] tested along with fuel pres and link and sync done JOE

While an ECU problem is certainly possible, it's VERY wise to start with the BASICS FIRST (Compression, Spark, Fuel Quality/Delivery/Pressure).

And ABSOLUTELY check the items Joe suggested (above)- especially since the problem seems to be worse when the engine is cold.

[Nitro29]

Would the Throttle Position Sensor be a possible culprit?

[JOE54]

dout it

[EuropeanAM]

dout it

+1... not impossible, but it's well down the list of likely causes.

[Nitro29]

Hooked it up to a computer and it is saying a temperature sensor is acting up. Hopefully this is on the right track.

[JOE54]

which one air or head both can cause prob

[QuickBullet]

You can check the temp sensor with ice water and nuked water! I just replaced my 1995 sensor and it made a World of difference!

[EuropeanAM]

Just a guess- air temp, displaying something close to a couple million degrees?

[Nitro29]

Air temp sensor was correct. Now it starts great when cold. Once warmed up, it begin sputtering when in drive with no throttle applied. I can run hard for about 7-8 minutes and then it shuts down... normally stays running, but completely drops rpms. I can take off again within about 10 seconds. Any ideas?

[QuickBullet]

Be sure to clean the orficed fittings in the intake for the MAP and Pressure Regulator!
Berryman or any Carb Choke cleaner with the little red plastic tube will do it!
HOWEVER, it sounds like you're running out of fuel!!!
Filters stopped up or pump failing???

[Nitro29]

I will try to get on checking that immediately. Will it hurt to open either pump up? Any parts I need to go ahead and order? I have checked the Fuel Filter and actually replaced it recently. Same for Fuel lines.

[EuropeanAM]

Pulse pump should have been rebuilt when fuel lines were upgraded (and primer bulb should have been replaced). You'll need a Part# 857005A1 kit, and about 1/2 dozen 816311T Radius-Head Tie Wraps.

VST is a little more tricky... and if you go in there, you will need to replace specific parts. Let's not jump there just yet....

One other note: Double check TPS adjustment, especially since you've replaced the IAT. Very critical that the procedure shown in the Service Manual be followed (exactly).