My 1988 R10 suburban 5.7 starts fine but stalls after 5 or 10 seconds, wait another 10 seconds it will start again and stall, every so often it will stay running for varying lenghts of time but will stall and start with the 5 or 10 second thing again, I removed the map sensor it idled rough but again only ran for 5 to 10 seconds, I replaced the coolant temp sensor, no change, any ideas?