Ford Repair: SPUTTERING OF EXHAUST AND CK ENGINE LIGHT, overhead valves, race engines

Question
QUESTION: HI,
I HAVE A 98 EXPLORER SPORT 4WD 2DR WITH A MANUAL 5 SPEED 6CYL (DOES NOT OVERHEAD VALVES)THIS VEHICLE HAS 300K MILES ON HER. I RECENTLY HAD QUITE A BIT OF WORK DONE. NEW HEADS AND VALVES, CLUTCH & THROW OUT BEARING, NEW WINDOW MOTOE,NEW DOOR LOCK,NEW EMERGENCY BRAKE ASSEMBLY AND A NEW RADIATOR. THE MAIN PROBLEM IS WITH THE HEADS. AT FIRST IT KEPT LEAKING OIL FROM THE #5 CYL AROUND THE GASKET...OVER 3 MONTHS THEY REPLACED IT 3X AND FINALLY IT STOPPED LEAKING...A FEW WEEKS LATER THE MOTORS CHECK ENGINE LIGHT CAME ON AND THE EXHAUST STARTED SPUTTERING AND A ROUGH IDLE.THE CODE READER SAID A PROBLEM WITH THE #5CYL SO I BROUGHT IT TO THEM AGAIN AND THEY CHECKED IT AND SAID IT WAS A FUEL INJECTOR. I TOLD THEM I WANTED A SECOND OPINION SO I WENT TO MY FRIEND WHO RACES FORDS AND BUILDS RACE ENGINES. WHEN HE CHECKED IT HE TOLD ME THAT THE #5CYL WAS ONLY GETTING ABOUT 80PSI AND THE OTHERS WERE AT 150PSI. HE SAID MOST LIKELY A BAD VALVE OR SPRING. I THEN BROUGHT IT BACK TO THE REPAIR SHOP ARMED WITH THIS INFO AND AFTER THEY DOUBLE CHECKED HIS RESULT THEY REPLACED THE ONE HEAD NOT BOTH EVEN THOUGH BOTH HEADS WERE REPLACED ORIGINALLY. WHEN I GOT THE CAR BACK IT STILL HAD SOME MINOR SPUTTERING BUT THEY SAID DONT WORRY ABOUT IT.ABOUT 2 MONTHS HAVE GONE BY AND I NOTICED IF I DONT WARM THE CAR UP FOR AT LEAST 10 MIN. THE CAR AFTER 2 OR 3 MIN OF DRIVING WILL HAVE A PROBLEM ACCELERATING KIND OF BOUNCING UP AND DOWN AND A GREAT LOSS OF POWER. AFTER ABOUT 5 MIN. EVERYTHING RETURNS TO NORMAL. ALTHOUGH THE LAST TIME THIOS HAPPENED ABOUT A WEE3K AGO THE CHECK ENGIE LIGHT CAME ON AND WAS AT FIRST FLASHING THEN IT CHANGED TO A SOLID CHECK ENGINE LIGHT AND REGAINED POWER. THIS PAST WEEKEND  I CLEARED THE CHECK ENGINE LIGHT BY DISCONNECTING THE BATTERY FOR 15 MIN. AND IT HASNT TURNED BACK ON .....YET. THIS IS MY QUESTION, DOES IT SOUND TO YOU LIKE A BAD VALVE IN THE HEAD AGAIN OR SOMETHING ELSE?.ALL THE HEADS WERE PURCHASED FROM A COMPANY CALLED NATIONAL HEAD REBUILDERS. HAVE YOU HEARD OF ANY PROBLEMS WITH THIS COMPANYS
HEADS? COULD THERE BE SOMETHING WRONG WITH A MOLD THEY USE? COULD THEY BE OVERBORING THE VALVES WHEN REBUILDING THEM. I AM AT MY WITS END WITH THIS REPAIR SHOP. ALMOST EVERYTHING THEY HAVE DONE HAD TO GO BACK TO THEM FOR ADJUSTMENTS. I HOPE YOU CAN HELP ME.
         REGARDS,
         DR. F.

ANSWER: Hello Doc, It is possible it could be a idle air control valve, which controls engine at idle or a vacuum leak from a line or pcv hose. You could get a can of carb cleaner and spray modesty around the top of the engine to see if there is a vacuum leak. If the engine idle goes up there is a vacuum leak, if it doesn't then there is no vacuum leak. Check the BBB for a reliable auto repair shop or dealership. The check engine light comes back on will help a shop to start a diagnostics. These are a few suggestions to possibly help. Thanks Tony

---------- FOLLOW-UP ----------

QUESTION: HI AND THANK YOU FOR THE REPLY THERE IS NO VACCUM LEAK AS FAR AS I CAN TELL ... THIS IS WHAT HAPPENS THERE IS A SPUTTERING NOISE AT IDLE ALL THE TIME FROM THE MUFFLER BT IT DOES NOT APPEAR TO BE IDLEING ROUGHLY. IF IT IS A VERY COLD DAY THE ENGINE WHILE IN NEUTRAL HAS A ROUGH ACCELERATION WHEN DEPRESSING THE PEDAL TILL ABOUT 2000 RPM. IF I WERE TO DRIVE THE VEHICLE WITHOUT LETTING IT WARM UP FOR ABOUT 5 MIN. IT WOULD ACCELERATE VERY POORLY AND ROUGHLY WITH A GREAT LOS OF POWER AND THE CHECK ENGINE LIGHT SOMETIMES WILL COME ON AS WELL AS THE CAR BOUNCING UP AND DOWN. ONCE THE ENGINE IS WARM THIS DISSAPEARS BUT THE SPUTTERING AT IDLE ALWAYS PRESENT. AS I MENTIONED BEFORE BOTH HEADS WERE REPLACED AND ONE OF THE REPLACEMENT HEADS HAD TO BE REPLACED A FEW WEEKS AFTER BECAUSE OF A DEFECT  AS ONE OF THE  VALVES WERE NOT OPENING AND CLOSING PROPERLY. .....WHAT DO YOU THINK?....PS I DID TRY THAT THING YOU TOLD ME TO DO WITH THE CARB CLEANER BUT DIDNT SEE CHANGE IN ENGINE SPEED.
         THANKS
         ANDY

Answer
Hello Andy, Has the check engine light came back on?  I am curious what the codes are. If the light comes on take to a parts store like a auto zone or advanced auto and have them read the codes, they will perform this service at no charge. Let me know  Thanks Tony