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98 454 xli erratic idle

rusty459

New member
"I have a 98 Silverton 352 mot

"I have a 98 Silverton 352 motor yacht with 454 tpi crusader's. when motors are started after a few minutes they will drop rpm's almost stall then pick up again run for a minute or so then repeat the same thing. So far I have cleaned the screws for the ign module, replaced fuel filters, replaced both IAC motors, cleaned oberg filters,disconnected the orange slave wire connecting the motors, and added new fuel and conditioner to both tanks. The condition does not happen above 1000 rpm's. The boat runs fine at cruising rpm's and even WOT. I also have a definate hesitation on the throttles when in idle and attemting to get the boat on plane. The hesitation only occurs for a second then the motors respond."
 
"Hate to say it but sounds lik

"Hate to say it but sounds like time to get a real scan tool hooked up to get some insight into what's really going on.....nobody's moved the distributors recently, have they?"
 
"Put scan tool on it no codes,

"Put scan tool on it no codes, distributors not touched. Thinking now maybe a pressure regulator. When i first got the boat has problems with a dirty tank. Thinking regulator may be clogged."
 
"scan tool - not a code reader

"scan tool - not a code reader - so you can see what the sensor outputs are.

Could be in the regulator as the ECM doesn't have any input from it. Fuel pressure gauges are cheap, just be careful hooking one up."
 
"Puy Rhinda scan tool on. No c

"Puy Rhinda scan tool on. No codes from ECM. Checked fuel pressure on both motors was 35 lbs, Also changed fuel pressure regulator. No change"
 
"So, what did the TP and MAP s

"So, what did the TP and MAP sensor readings show?

The MAP will work similar to a vacuum gauge and is useful in a similar manner. The TP tells the computer what it thinks you are doing with the throttle - if sticking or misaligned, it can generate idle instabilities/hesitations/etc."
 
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